Go back 2 pages in this thread (page 21) -- near the bottom of the page, Hegelian has a long message with info on his "$1400 MATY PC" -- I followed much of his list (different mobo and video card and newer CPU), but came in right around $1k using a combination of new stuff and existing parts (video card and HD) from my old PC. You could follow his info while modifying it to better fit your budget (ie, smaller HD, cheaper processor, etc). The advantage of following his list is that pretty much everything is upgradeable, so you could expand/improve the PC as time and your budget allows.
Another handy source for info on building your own PC is the "DIY PC" blog on ZD Net. Here's a link to a recent entry on building a sub-$1k gaming PC:
http://blogs.zdnet.com/hardware/?p=1147Enjoy! and certainly come back to this thread for info as you progress -- I have a feeling it'll be around here for a long time.