The Location of fictional planets in this (or other) galaxies

I think Vulcan is supposed to orbit 40 Erandi.

Actually, the Spelljammer setting for D&D did cover the entire solar systems for several worlds, but I never much cared for it, so I can't give you details. I can however assure you that the D&D planets are not in the same universe as real-life earth, unless the laws of physics fluctuate from galaxy to galaxy. What with Toril being a solid planet the size of Jupiter that doesn't seem to generate the appropriate amount of gravity a hyperdense planet that size should.

Babylon 5 tended to use a pretty straightforward nomenclature. Star and sysdtem were most often called [name] and the corresponding planets [name] [roman numeral]. So Proxima III was the third planet from the sun in the Proxima system. Though settled planets, especially important ones, often had proper names such as Centauri Prime, Minbar or Z'ha'dum.

"If you're going through hell, keep going."
Winston Churchill

Toril is actually the size of Jupiter? News to me.

Are we talking just comic book? Or various other media? Movies? Games (not just computer)? What?

The BattleTech community has a reference of several thousand planets. You can look them up here: http://isatlas.teamspam.net/

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According to Spelljammer.org Toril is a Size E planet, which means it has a diameter of 4,000 to 10,000 miles. I believe this makes it similar in size to the Earth.

It was something people figured out after they actually looked at the various maps given for the various continents. If you add all the distances given together, the planet comes out as gigantic.

"If you're going through hell, keep going."
Winston Churchill

The AD&D settings not only aren't located in the Milky Way galaxy; they're located in a universe in which galaxies don't even exist.

As EisenRegen and others imply, the AD&D multiverse (specifically as described in the early '90's Spelljammer products and related material) has a somewhat consistent set of physical laws regarding objects in space, but those laws bear almost no relationship to those of the real world.

In this setting, earthlike worlds such as you're describing exist on the Prime Material Plane, which consists of an infinite, bottomless, surfaceless ocean of a flammable meta-element called "phlogiston" (a term lifted from some early models that attempted to explain real-world thermodynamics). Within this phlogiston, immense, round spheres known as "crystal spheres" (a concept lifted from some medieval ideas about the structure of the universe) exist. Inside most of these spheres is a vacuum of space in which various bodies called "planets" orbit a central body.

AD&D celestial bodies, rather than being characterized as stars, terrestrial planets, Jovian planets, and so on, are described by their elemental nature (earth, fire, etc.) and size (on a scale ranging from A to J). A fire body, particularly of size J or larger, is generally referred to as a "sun," and many crystal spheres, including the one containing the planet Toril, have a sun at their center. Earth bodies are usually habitable worlds much like our earth, including atmospheres. (Worlds without breathable air are rare and are known as "voidworlds.")

So far, these planets aren't all that different from ones that might exist in the real universe, though the categories used to describe them are different (most gases are undifferentiated, breathable "air" rather than the mixtures of different, recognized elements that make up real-world air, etc.). Where this setting really differs wildly from reality is in the way gravity works. In the real universe, the gravity an object generates depends on its mass, so that large bodies have high gravity and small bodies have low gravity. Further, gravity varies with the square of the distance between objects.

In the AD&D worlds, gravity is constant. All objects, regardless of size, generate the same force of gravity. Where a person might weigh 150 pounds on the (massive) real earth and only a fraction of that while on a (low-mass) spacecraft in space, in the AD&D setting, the person weighs 150 pounds no matter where he is. Further, rather than collapsing objects over a certain mass to a spherical shape, as in the real world, AD&D gravity conforms to the shape of objects. A sphere's gravity pulls toward a point at the center of the sphere, but the gravity of a galleon-shaped ship in space exists in a plane running parallel to the deck, so that a person can stand normally on the deck while in space. (The gravity plane is two-sided, so a person could also walk along the bottom of the ship.)

All of this explains how even a body of the same density as the real earth but much larger could exert the same gravity in an AD&D setting as real-world earth gravity. It's because that setting's gravity simply Works That Way. This isn't very realistic, but at least it's relatively consistent within its own milieu.

Okay, I'm embarassed that I wrote all that purely from memory. Man, did I ever waste my high school years. I'll stop now ....

Actually, I think it's perfectly valid. It's what you'd call fantastic realism. The rule regarding gravity (ie. there being no difference between weight and mass based on gravity) is obviously not real or even realistic, but it's consistently applied. Like I said, I never really got into Spelljammer, but slowly there are a few things coming back to me.

"If you're going through hell, keep going."
Winston Churchill

Toril's biosphere is a TARDIS.

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TeamSpam's site also has the Inner Sphere Cartography Society attached to it.

You can pull down PDFs of the whole Inner Sphere (and Clanspace).

http://iscs.teamspam.net/

The last BattleTech boxed set came with a very nice IS map by one of the ISCS contributors as well.

Clicking on the linked image above will take you off the City of Heroes site. However, the guides will be linked back here.