I found an E6700 on eBay: www.ebay.com/.../150966953115
Dual cores can make a solid difference in performance, so I'd recommend one.
I'm not sure that your mainboard supports the P4, which is a weak processor by today's standards, even though it is of the correct socket. You'll be much happier with a faster, cooler-running Wolfdale CPU like the E6700, and the board is designed to use it.
I had no idea the Wolfdale was discontinued, as there are various motherboards still produced.
