AGP video card recommendation for SFF PC

I built my girlfriend a SFF AOpen PC and the only things that went in the machine from her old computer were the CD burner and the video card (GeForce FX 5200). Here are the specs:

AMD Sempron 2500+ (1.75 Ghz)
2 x 512 MB Corsair ValueRAM
WD 80GB IDE HDD
LG 16x10x40 CD-RW
AOpen EZ18 (220W Power supply, MB w/ NVIDIA nForce2 with IGP Northbridge MCP-T Southbridge) see specs here
GeForce FX 5200 PCI (free AGP port right now)
Hi-speed USB Hub (powered...phew)

I recently got her "The Movies", but as you can expect, it ran pretty poorly on the video card. I'm thinking that maybe an upgrade to a GeForce 6600 may work, but I don't want to overload the small power supply. I checked out some older reviews of AGP video cards on Tom's Hardware, and it seems that peak system consumption on systems running 6600's stayed below 220W, and that was with a more powerful processor eating more power I presume. I would prefer to go with a 6600GT or vanilla 6800, but I'm thinking that might be crossing the power consumption line. I'm also very open to ATI suggestions, but I seem to recall that at the time of release, the 6600 hit the sweet spot of power consumption vs. performance vs. price.

I'd appreciate any help/advice you can give me, thanks!

Oops, I guess I wasn't being clear. "The Movies" is a game from Lionhead Studios. Video replay doesn't concern me much. I'll look into that video card - any idea of the system power consumption with that card in?