3d modeling is a field that is covered by many different types of software. If you're taking a 3d class at your local high school (or college), then you'll likely be issued a paid program. (Solidworks or autodesk for drafting classes, Maya for 3d animation... the list goes on and on.) However, many of the new and upcoming modelers (who don't have the ability/desire to spend (what I'd say is an exorbiant amount of money)) use a free program named "Blender". (Several others use wings, free versions of maya, gmax, sketchup, etc) You can find out more about 3dmodeling programs (or cad/cam programs) on wikipedia
3d
http://en.wikipedia.org/wiki/3D_computer_graphics_software
Edit: Also as nintendude mentioned, some guys have the ability to rip files straight from the game, which makes the rest of us insanely jealous.
Blender is available for download here
http://www.blender.org/download/get-blender/
If you're just starting, it might be worth it to try out and learn the new 2.51 beta version. (As that is the most recent version.) 2.49 is the latest stable version.
You can probably find a local class being taught in your area, depending on how remote you are, or you can teach yourself online.
This wikibook teaches one a good deal about the user interface of blender.
http://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro
In terms of modeling, I'm afraid that's pretty hands on work.
Cheers!
Edit #2: Rundown talks about 3d modeling
http://405th.com/forums/index.php?showtopic=25019&st=0&p=405307&fromsearch=1&#entry405307
Edit #3: Sorry I meant the 2.5 alpha 2 version....