About AGP and PCI-E cards?

Hi Guys! I have two cpu with one pci-e and an agp both pentium 4 3.0 with HT and 1 gb ram. My pci-e cpu has a 7600gs card and I was kinda wondering if I buy a 7600gs agp, will they have the same performance. Actually it was my bros cpu and he was asking me for a good agp card for his bday. Thanks!