PCI 9400GT vs PCI-E 9400GT

Hi, I'm new to the forum and I have a question about a video card. I am NOT a hardcore gamer and I don't need a very powerfull card but I do play some old games now and then. I have an old Dell desktop:

OS-Windows XP Pro/Windows 7
PSU-575W (upgraded from 230W)
CPU-P4 @ 2.8ghz
RAM-2.5gb DDR2
HDD-SATA 160gb+250gb external
GPU-ancient ATI radeon 9250 (PCI)

Because my current card does not fully support windows vista/7 or directx 9 O_o I decided to upgrade but because I have an old motherboard my only option is a PCI which is not so great for gaming but is more then good enough for me. I found a 9400GT 1gb DDR2 PCI by EVGA that is compatible with my system but they also have PCI-E version of the same card with 1gb DDR2 but it costs 15$ less, I know that PCI-E is much more advanced but how much difference does it make in games since both cards use same GPU and RAM, I wasn't able to find benchmarks on the card though. Does anyone know the difference in performance between those two? Any help apreciated.

Thanks.

the best the pci vga can handle is 2d graphic