to get back to the gui screen, follow the instructions you used to get into command line mode... in reverse
su, then "emacs /etc/inittab" and when your in the file change the line that says "id:3:initdefault" to "id:5:initdefault" and press ctrl-x ctrl-c to exit and it will ask to save changes just press yes...when you reboot you will boot directly into console.
(the above quoted heavily and changed slightly from DrOzz's post)
quake3 = now that you have the nvidia drivers installed, reboot and try again. it *should* work.
ut2k3 = the retail version of UT2k3 has the linux installer on the 3rd disc. There isn't a download for it. At least, not a legal download for it...
kazaa = I've never used kazaa..
half-life and mods = again, you need a retail copy. wine from winehq will work (as previously noted), BUT, I found Transgaming's Winex
to be far easier to setup,install,use. It'll cost you $5/month, but it will allow you to run a mulitide of windows games - including many that won't work w/regular wine. I found it to be worth the purchase price, you may not
edit: I hang out in #cofr on east.gamesnet.net in the evenings (the gamesnet irc network has many different servers though). my irc nick is, unsurprisingly, MMaster, and there are other linux guys willing to help even if I'm not there. just mention my nickname...