$200 for a vid card to pair with a 1.2GHZ Athlon...
The fastest you can get right now in that price range is a GF2, and that comes in at about $150 give or take depending on which board you go with. Any particular features you would like- ie video out, DVI etc?
The most feature rich card you can get for that right now is the Radeon 32MB DDR. The Radeon 32MB DDR is nearly as fast as the GF2, has very solid 2D even on trinitron tubed monitors(which is a weak point for the GF2) and the best consumer level video acceleration you can get(DVD, MPEG1, pretty much all the PC video formats but not quite all).
The thing is, that is all right now, not in two months🙂
Two months from now we will be looking at the NV20 as the king of the hill which should have a price impact on all the lower offerings. It is possible that the GF2 Pro could drop into the $200 price range in that period of time. The GF2 Pro is considerably faster then either of two I mentioned above, although it won't look it next to the NV20(which is likely to be in the $350-$450 range, possibly going as high as $500).
Also, what types of games do you like to play and what else do you do with your system? If you don't do anything 3D, forget everything I have said and buy a G400, you won't regret it. If you only occasionaly game, then the Radeon 32MB DDR will likely be your best bet even in a couple of months, as it has solid 3D performance and overall higher levels of 2D quality, and the speed difference won't be that big of a deal to a casual gamer(you may have to run 1024x768 32bit@ 60FPS instead of 100FPS).