look into ATI's 9600XT line, unless of course you hate ATII don't hate ATI. It's just that in the beginning of the graphics card war, some of the games just would not run on an ATI, and many of the others would run, but with problems. Then came the battle between 3dFX and OpenGL support which ATI fully supported 3dFX internally, but OpenGL was an external dll which ran in computer memory and not in the graphics card...thus slow. It just seems to me that ATI has made the wrong choice each time. That's how nVidia found it's niche...supporting OpenGL internally so that flawless graphics for Quake was a reality...they also worked with Carmack as did Microsoft. Much of the really good stuff in DirectX is in there because of nVidia and Carmack leveraging their power against Microsoft to make sure that the industry get better as it grows. From what I can see from Thief3 and it's use of Pixel Shaders for shadows, the difference in the new games will be astounding. Quite possibly a bigger jump than we saw from Doom to Quake, or even from Quake to Quake2. I'm sure Doom3 will include a lot of attention to detail...a flying flaming skull isn't very scary if you can see through it's cheekbone, or a monsters face is made up of just five sides and the nose is just painted on.
I would not upgrade my graphics card for just one gameNo, I will have to dissagree with you there. Doom3 or one of the other games coming out this year (HL2, TF2 for starters) will definitely require a better graphics card and I guarantee you will find it worth the money.
Let's Rock!