depends also on when you want to spend it. a geforce mx will get you most of the speed of a gts, and can be found for $100 or so oem. if you can find a gts for under $200, i'd take that. the speed is there, the nt5 support is there. it does have issues with texture compression and also the 2d quality can be poor depending on the manufacturer. the v5 is a good performer, not too sure about the nt5 support, ask someone who has one, and it seems like the driver updates are getting more performance out of it than nvidia does. plus it makes half life a dream, what with very good FSAA that the geforce and radeon just can't match. the radeon is sorta a wildcard. the retail DDR versions are very good with win 98, have great dvd support, plenty of speed. i'd also consider them slightly more future proof than a geforce, since it has triple texturing and a more programmable t&l than the geforce. but the nt5 drivers suck big time. and the oem/lower priced versions don't have near the speed.
okay, heres my recommendation: the geforce mx. it is just as fast as a gts with a celeron 400, firingsquad did a comparison of cards with "low end" processors a while back, it performed well. its cheap, leaves you with some money left over, which is always a good thing. the drivers for nt5 are solid. i did have issues with the 3 version drivers under win 2k (bluescreens attributed to nv4disp.dll... my voodoo 3 never had probs) but since then they've cleared up.