Yes, the 7600GT is the perfect match for your processor imo.
some clarification about it...
The processor and the graphics card should match each other in horse power.
If the one is far superior than the other the slower one will hold down the faster.
This is often called as "bottleneck".
So in your case the 9600 is holding down the P4 3GHz, but the 7600GT is the perfect match for it.