best upgrade -- am i cpu limited?

hi i have a socket478 p4 2.2ghz, 768mb pc133, a geforce4ti 4200. I also have a dell inspiron6000 with 512mb ddr2, pentiumM 1.6, and a 128mb x300. so they are pretty much equivilent gaming machines, well my lappy is better at HL2. Anyway i was going to get a x700pro for my desktop... i 've been able to price it at $99 retail, sometimes. is this worth it, or will it be processor limited? should i stick with my ti4200? I also have a athlon xp2000+ box that is pc133 and has an agp slot, but i keep my video card in the p4 box, cause i think it has a bit more power, thoughts?
thanks alot,
- justin