Yes. PCI will work, and with the GF2 MX being AGP 2x/4x compliant it won't have a problem. Yes, the P4P800-E has an AGP 8x slot, but it's backwards compatible with AGP 4x.
Personally, I really love the Abit IS7 (I have the IS7-E), and you might consider it as it's got a similar feature set to the P4P800 series, and especially if you're looking to overclock. It also runs a little cheaper.