If your computer is socket 939 then you can't really upgrade it as a 4200X2 will be as good as it gets (o.k there are 4800s but they cost an arm and a leg now). If you have DDR Ram, then it's a socket 939, but if the RAM is DDR2, then it's at least an AM2 board. Anyway you're going to have to go to the HP website and see the CPU support for your particular model. I doubt you will be able to do much better than an Athlon 6000+ without a hacked BIOS, but check the HP website to be sure. Also, there are currently 3 versions of the Athlon 6000+. There are two Windsor models with the first one being 125W and the second being 95W. The latter is preferable. The third version is the Brisbane model.