Upgrading cpus for dells is tricky and involves some guesswork. Looks like your board has a g33 chipset. I would go for a used e6600 at 1066 fsb or even a q6600 quad core if you get it for around $110. Starmicro carries oem cpus new. Your board probably won't work with 1333 fsb cpus. You can also post your question on one of the dell forums and see what others have used. I would post a request for a used one on craigslist or anandtech's for sale forum. Used cpus can be had much cheaper. The e6600 has been listed for around $70-80 recently.