I'd say layering is your best bet.
BUT! I've never used Photoshop long enough to figure things out. Still, the techniques are -pretty- much the same between art-media programs, though the exact methods to -use- those techniques are what varies.
So, yar. Layering. S'my suggestion. Hopefully someone that has a better idea of what they're on about can come along and give a better one, though. 
it's not hard, just open each picture individually, if it's a white bacground, you can just use the wand to cut out the char itself, paste on a new picture, a white bacground, then using layers, you can decide if one is behind another.
Im not sure if you're asking for an in depth explaination or just where to start. So I'll just give you a quick beginners run through, if you already know the basics then disregard. Basically just open up each individual image of all of the toons you want to use and set them aside. Then create a new image (file > new) and make it the size you want. (I recommend somewhere around 1024x768 pixels based on the size of the screenshots that CoX creates).
Then you will see in your toolbar (which is by default in the upper left corner of the photoshop window) a button for your lasso tool (it's the second from the top button on the left column).
This requires a fairly steady hand but with that lasso tool, you can cut out the toon from the screenshot. A little tip is that you can click and hold the mouse on the lasso tool button, and select the polygonal lasso tool instead, which basically uses straight lines to cut out your image. This helps because you dont have to be as precise with your hand movements, but if you go very slowly you can avoid any jagged edges in your cut-out. There is also the magnetic lasso tool which takes away alot of the precision needed while cutting out an image because it kind of guesses where you want to cut out, but I've found this to be more of a hinderance than anything, but it might be the way to go if you're not used to using the lasso tool.
Once you have the entire toon carved out, you'll see a dashed, flashing outline around the toon. Then select the move tool (which is the button on the very top of the right column in the tool bar) and just drag the toon to the new image you created.
Repeat with each toon and you got it. Each toon will be re-created on the new image as layers, and each layer can be controlled in the layers window on your right hand side.
Let us know if this is what you were looking for, or if you need more help.
Depending on what you're going with, actually, I wouldn't just create a whole new image.
What I usually do for stuff like that is create (or steal..) the desired background for what I wanna go with, then paste everything onto it as appropriate. But that's just my helpful little nudge there.
Other then that, I think Fueled has the situation covered!
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Okies Photoshop question
I have a bunch of indvidul Charater pictures or lil toons , but I want to merge them together in a group shot (some standing behind others )
any idea how to do it ?
any help is appreciated (greatly appreciated )
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Read and try this...
LJ
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Read and try this...
LJ
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Well there you go. Pretty much everything you need to know with much better explanations and even screenshots of the tools and what they do. Nice find LadyJudgement.
Yeah I was gonna write it up, and then I thought, umm I'm sure someone's done this way better than I could explain. AND with visuals... aduh!
And now I can go play, having done my good deed for the day.
Your 2ND good deed! 
thanks guys that perfect !
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Okies Photoshop question
I have a bunch of indvidul Charater pictures or lil toons , but I want to merge them together in a group shot (some standing behind others )
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Aside from the many digital-mechanics of doing this as mentioned above, there are some more basics to keep in mind:
1. Have the camera shots that closely match up in /size/ and /framing/ for each of the characters you plan on creating a montage compilation with. Nothing looks funnier than a giant headshot matted-in standing next to a dimunitive body shot of the person in front. ALL the subjects standing in the frame should be a complimentary size to one another.
2. Choose the same 'time of day' for each subject... or as close as you can get, so the lighting and direction of those key lights closely matches for each character. There is nothing good about having a mixture of both day and night shots of each subject standing together. It just won't look right and even the color-temperature will be off. Keep in mind that Co* has 2x the speed of a Day-Night Cycle as of most other MMOGs. ie: Most MMOG Day-Night cycles are 72 RL minutes to complete one cycle. For some reason the Devs for CoH chose 2X this pace or 36 minutes(!) for one cycle. So your optimal timing-window will be smaller. And ALWAYS insist upon using /Day/-Cycle photos and /Day/-Cycle backgrounds whenever possible. Nighttime is horrid on lighting-levels for this game!
3. Place and frame your subjects complimentary to each other in terms of direction. That is... if you have any standing in straight-on positioning, those subjects should stand in the center. If they are eighth or quarter-turned ot the left, they need to be on the LEFT side of the frame. Eighth or quarter-turned to the right.. the RIGHT side of the frame, etc. Think of it as how you would stand your subjects in one giant group shot so all are facing the direction of the camera lens.
Good luck.
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Okies Photoshop question
I have a bunch of indvidul Charater pictures or lil toons , but I want to merge them together in a group shot (some standing behind others )
any idea how to do it ?
any help is appreciated (greatly appreciated )
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Read and try this...
LJ
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Yay you found a website for it! I was going to suggest the quick mask tool. much much much easier than the lasso. You just paint and erase!
The above techniques are good, but extremely meticulous. Hand-selecting with the lasso tool is beyond my personal patience level.
Assuming the background is a solid color (such as white), there's a method that uses only a couple clicks.
1 - Create a new image the size you desire.
2 - Copy/Paste your target image into the new image. It'll appear on it's own layer.
3 - Using the magic wand, select the background and hit 'delete'
4 - (THE MOST IMPORTANT STEP) Select Image > Matting > Defringe. I usually use a setting of 1 pixel. This will remove the little white specks that a magic ward can't always select.
All told, compositing will take about 20 seconds per image.
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4 - (THE MOST IMPORTANT STEP) Select Image > Matting > Defringe. I usually use a setting of 1 pixel.
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One slight correction to this which I have on my copy of PhotoS:
Layer > Matting > Defringe.
Use Defringe often. Make it your bestest layering friend evah.
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The above techniques are good, but extremely meticulous. Hand-selecting with the lasso tool is beyond my personal patience level.
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Yeah I use to hate the lasso tool also, until aduh I realized if you click the icon that looks like 2 boxes together, the "add to select" tab, it makes it so that you can select little sections at a time, and they all add up together.
If you mess up, press & hold down the ALT key, and the lasso becomes a minus tool, and you can take out sections. Using this method, I can breeze through most intricate shapes.
Infact I tend to work in reverse, I lasso the whole figure in quick ovals, then go back, and minus where I went too fast.
Okies Photoshop question
I have a bunch of indvidul Charater pictures or lil toons , but I want to merge them together in a group shot (some standing behind others )
any idea how to do it ?
any help is appreciated (greatly appreciated )