If you put a P4 in, you'll need DDR, as it won't accept the SDR that's in you Dell. Another problem with Dell's and Compaq's is they use a specific brand of memory, not generic, to get you to buy thiers. I don't know if you'll be able to use the Dell power supply, too. But, if you like to Ebay, I built a P4 system for my wife for Christmas, just being patient and only bidding at the last couple of minutes..got her MB for 48, processor for 30, memory for 26, case I bought locally for 60, and it came with a 350 watt supply. Had an old Matrox 64 Meg AGP card lying around, and took everything else out of her old comp. All in all took about 3 weeks (with shipping)..its only a 2 GHz processor, but she uses it for her home office and internet access.
Mike