Get SuSE or Mandrake or something. Gentoo is seriously non-trivial to install, especially for a new user. SuSE and Mandrake will hold your hand through the process and make it pretty painless. Ubuntu and Knoppix have the same ease-of-use involved. Gentoo is going to be jumping in the deep end, same with Debian.
Hey; I write code for a living (webapps, mostly), and I'm interested in helping out with The Dark Mod. I can dedicate 6-7 hours a week, give or take, to the project. (Basically a day of coding, for me). I haven't dug into Doom3 coding, yet, save some research for a mod I was planning on, but the AI looks incredibly powerful, and I'd like to see what evil can be crafted for the guard AIs.