Taking a slightly different approach to this....a 3.4GHz P4 is powerful enough to get the full benefit from any graphics card up to at least an NVidia 6800GT or ATI x800xt.
So if you are planning to use a graphics card that is as powerful as anything up to those mentioned you have no problem.
For the record have a 3.2GHZ P4 running at 3.6GHz and an ATI x800xt and that works very well indeed.I can play just about any recent game at 1280x1024(and a good many at 1600x1200) and maximum detail with a moderate degree of AA/AF applied although there are some that make my system grind to a complete halt!
Like the F.E.A.R demo at 1600x1200 with everything on maximum with 4xAA and 16xAF and "soft shadows" enabled......an average of 8fps,lol.....but it looks fantastic!!!