Yeah, the 945P Intel chipset will definitely support the Pentium D, Pentium 4 HT, and Celeron D. Just make sure the P4 is compatible with socket LGA775 that is on the motherboard. Most processor packaging or on the website you want to buy it from will tell you what socket the CPU supports. I'm sure that most are the newer LGA775 anyways.
I recommend the P4 with Hyper Threading if you want a P4. Otherwise, a Pentium D is nice to have because of it's dual core capabilities.