Could you not scrounge up a smidgen of $ and get these. http://www.newegg.com/Product/Product.aspx?Item=N82E16819116036http://www.newegg.com/Product/Product.aspx?Item=N82E16811119106http://www.newegg.com/Product/Product.aspx?Item=N82E16813131030Rhttp://www.newegg.com/Product/Product.aspx?Item=N82E16817153023
$211ish total. unless you need ram. then add like $40 for 2GB PC6400
That setup there would get you running without bottlenecking the GPU and allow you to enjoy most all the games out there at deceint speeds/details.
My p4 3.0 is overclocked to 3.3 and still bottlenecks my 7800GS AGP. So moving up a cpu is a much better upgrade then just keeping hte p4. Its ran its life a long time ago.
Currently your 7600GT was almost on par with my 7800gs.. Both good cards, but again your reaching the end of your cpu's abilities. I once upgraded a P3 933 from a GF2MX to a Geforce 3 TI 500. It got faster but only by like 20fps.. then when i got a p4 1.8 it unlocked the card and i was over 100fps faster in most of the games I played at the time.
The ATI card is a great card.. but its almost faster alone then your P4 lol. I would say get a slightly newer setup like this. and keep the 7600GT till you can afford both. The 7600GT will even get a speed boost with a new CPU.