Anything with decent opengl support should work, and that pretty much includes every nvidia card from the Riva TNT on up. (when I started mapping for RTCW, I used a celeron 300 and a TNT1, which was painfully slow, but not impossible). A Geforce2 should be OK, but you will probably want to keep cubic clipping on most of the time, and use low texture detail in the editor. If you want to work on really big complex maps, you will probably find it quite painful.
There isn’t any official documentation that doesn’t come with the editor. However, there are a lot of good resources on the net, I’d suggest checking the sticky threads at the top of this forum.
edit:
sock did do an update of the Level Designers Reference that comes with the editor. You can find it here: http://www.planetquake.com/simland/ldr1_1/default.htm