I'm not an expert, but I don't think it's a driver issue. Win7 should have whatever drivers it needs natively. I think the real issue is your old graphics adapter doesn't meet Win7's hardware requirements--particularly DirectX 9 and some minimum pixel pipelines support.
FWIW, I've upgraded a few 8-yr old Dell Dimension 4600 computers with Win7 and new GeForce 6200-based AGP8X graphics cards from newegg. (They were upgraded at different times, so brands varied from EVGA to Jaton to something called Sparkle, with 256 or 512MB ram.)
play ms pacman The D4600 came with integrated graphics and an empty AGP4X slot, but the integrated graphics doesn't support Win7 Aero effects. Dropping in an AGP4/8X card enabled Aero, bumped the "Windows Experience" graphics score from 1.0 to 3.6, and none of the cards required anything other than Win7's built-in drivers.
YMMV, but I think all you need to look for is a GeForce 6200 or better chipset, or whatever the equivalent would be from ATI.
Dan