So long as it's a 512MB version, though your P4 is going to be a huge issue in anything that isn't heavily GPU-intensive. Depending on your settings you may see zero framerate increase in CSS, even.
Look on the forums here and try to grab an HD3870 for $60 - $65 shipped. That would at least get you better performance now that would burry your 7900GT and isn't too far behind an 8800GT anyways.