theres no point in having a PCI-E slot with such a old CPU.
you already have a 7600GS?
your CPU is already bottlenecking your 7600GS... using a even faster GPU with such a slow CPU wont change much.
besides replacing your entire system... id say your only other option is upgrading the CPU instead.
though, since your using a 2.2ghz(witch probably realy old) chances are im guessing your uisng a APG 4x motherboard, witch may or maynot have Pentium4 "Prescott" support. ->go to your mothebroard manufactuers website and check there CPU support list.
here is a 2.8 Northwood P4 though, witch may be compatable for example:
theres also a 3.0P4 presscott there for similar price, but like i said it may not be compatable with your board....
...if your board is only AGP 4x with 533 Max FSB support... you may wont to just make due with what you got now, untill you can upgrade your entire system... beacuse if thats the case... your motherboad will still hold you back even if you upgrade your CPU or even GFX Card.