New video card for XPS GEN 4

I have an XPS Gen 4 Pentium(R) 4 CPU 3.40GHz.  I am trying to run some newer games (like Crysis) but could only run them at lower graphocs levels.  I upgraded the RAM to 4 GB and this did improve gameplay a lot.  I was thinking about upgrading the video card which is currently an ATI RADEON X800 XT 256Mb which came with the system.  Will a newer video card (not a high end expensive one) have a significant improvement in gameplay?  Which video cards are compatable with this system?