That's an old motherboard that may not work with core2 duos. I would post your question on one of the dell forums. If you decide to go ahead and try it anyway, I would lood for the e6400 used for around $30. If that works, then the q6600 might also work. Don't invest too much in such an old system. I never recommend upgrading a dell system with a newer cpu. Look for used cpus on craigslist or anandtech's for sale forum. Make an offer; don't spend too much. The lowest price for the q6600 I've seen is $70 for the cpu only. It only runs at 2.4 ghtz. People have used it alot as it overclocks well, but your dell boad won't permit overclocking. And you may also have to upgrade the heatsink for a quad core. Do some more research first.