If you decide on a cpu upgrade, then it MUST be 400/533 capable. Most cpu in that 478 socket type will support 400/533 cpus. Howver, don't fall for 533/800 one, that maybe a bios got'cha, even if it supports 533, the bios itself MUST be the latest before trying anything. While, I think your stock cooling will be fine, once you go beyond a 2.4ghz abilities of the cooling setup, I think the best you could do 3.0mhz cpu, IMHO provided all the specs fall into place, otherwise, you're 2.6 or 2.8mhz maybe the limit. If this case is so, why even brother, other than learning experience. I suggest you visit the Intel reference white papers for specs of opus in that class, further compare the cpus. The best you can ever do cpu wise is 3.4mhz, but I'm sure that's not supported(guessing). As Robert stated, cooling becomes an issue. But, overall that can be addressed, but also the age of the system comes into play. I believe the dell 8200 psu is not generically easy to replace, its one of the Dell's unique PSU(open to correction). Take all this into acct. it maybe more costly than you think for simple results.