Can my older PC benefit from a graphics card upgrade without or with a PSU upgrade?

After reading some of the related posts here, I'm wondering if it's even possible to adequately upgrade my graphics card. I'm hoping for an inexpensive way (<$250) to dramatically boost my frame rate while playing WoW on a 4-year-old PC:

Pentium 4 2.53GHz
1.5 GB RAM
Radeon 9250
mobo: Synnex 0406 (AGP)
PSU TC Star 400w, 14A on the +12V rail
17" Monitor at 1024x768 (may upgrade monitor if new AGP card permits good performance)

Current FPS in WoW is barely playable, even at low graphics settings. I get about 20 FPS if i'm in a low-population area, but this drops to 8 or even 6 in some raid instances.

1. What's the best card I can get with my current PSU, and how much of a Frame Rate improvement might I expect?

2. Alternatively, if I upgrade my PSU, how high level of an AGP card can my CPU and motherboard support?

I'm not expecting top-end performance. I guess I'd be satisfied with 30 FPS in a raid environment with mid-level graphics settings. I'd prefer not to buy a new PSU unless it's necessary, or if it allows me to get good FPS with high-level graphics settings.

well potentially your system can upgrade to the x1950 AGP cards. However this will require a new PSU.

Also your cpu will bottleneck that card a fair margin.

Im thinking your best bet would be a x1650pro/xt or the 7600GS/GT. Again, these may require you to spend a bit more money for a better psu.