The problem with your PC is also the fact that it s P4 2.8Gz. That is basically a huge bottleneck.
Below are benchmarks of the Radeon X1900XT with various different CPUs. Your single core P4 would rank at the bottom between the Intel Pentium D 805 and the Intel Celeron D 351 (both of those are dual core CPUs).
The X1900XT was around when nVidia had the GeForce 7xxx series which makes this powerful card two generations older than the GeForce 9xxx series (your weak 9500 GT).