Edit: scratch previous comment
P4i65GV features the "A.G.I." slot, which is not a real AGP interface. Its an AGP connector wired to the PCI bus. This pseudo-AGP slot will have limited or no compatibility with anything newer than GeForce 7 or Radeon 9 Series, as shown in the VGA support list on ASRock's website.
At any rate, GeForce 7600 GS is superior to Radeon HD 2400 PRO in gaming performance. The only thing Radeon HD 2400 PRO would give him is superior video decoding.
If he wants a better card for gaming, he'll need HD 2600 XT or HD 3650 at a minimum, except for the fact that NONE of these are going to work in that pseudo-AGP slot. He's not even getting half the potential of his 7600 GS because its effectively working as a PCI video card.
Bottom line: time for a complete upgrade.