Trying to decide on a video card upgrade and cant decide.

System:
MOBO-MICRO-STAR INTERNATIONAL CO., LTD MS-6540
Processor-3.00 gigahertz Intel Pentium 4
OS-Windows XP Home Edition Service Pack 2
Current VC- NVIDIA GeForce 7600 GS
Current RAM- Slot 'A0' has 512 MB Slot 'A1' has 512 MB1
AGP SLOTS NOT PCI-E
I do not know what PSU i have.

Budget: -$150

Uses: Gaming, movies, work.

I was considering a x850xt, but still trying to get some recommendations.