Help! Upgrading my old PC.?

I have a Pentium 4 2.4Ghz PC, in an ECS 865GV-M3 motherboard, with an ATI Radeon 9250 128mb Graphic Card. 512mb RAM. My motherboard is AGP capable only.. Can you guys pls help me, I want to upgrade my AGP Card.. A local store here in our place, sells GeForce FX5500, an ATI x1550, and a GeForce FX5950 ...can you guys give me suggestions on what to buy or give me info on the right AGP with hi performance for old pc's like mine. Thanks a lot.