Is a P4P800 SE compatible with an Intel Pentium D 805?

So is a P4P800 SE mobo and a Intel Pentium D 805 533MHz FSB LGA 775 Dual Core EM64T Processor compatible or not?

As somebody already mentioned, No. The P4P800 is a socket 478 board and the Pentium D 805 requires a socket 775 board.

If you're looking for inexpensive options for the Pentium D, the ASUS P5LD2 line shows some promise. I didn't reasearch my options much, I just went for a board that was compatible with the D 805. I have had good luck with the P5LD2 so far. I have been able to overclock my D 805 by 35% with little else than an aftermarket HSF. Even if overclocking is not your thing, it supports HD audio, SATA II RAID (including Intel Matrix RAID, which sounds interesting), DDR2, and PCI Express - your standard 945/955 chipset goodies.

I don't know if you're hung up on wanting a board that supports Conroe too. Personally, I am going to wait until it has been out for 6-8 months and there's a crop of new boards to support it.