i am going to post this again:
While THG has articles on updating oem pc's its a waste of time and money.
if you have a low end dell, hp acer or what ever do not waste your time. Its an endless cycle of upgades and in most cases you be better of ebaying the computer and starting over.
typcially one wants to upgrade the gpu but the psu is too small, next you want to oc the cpu but the bios sucks. Bottom line is once you starting replacing psu's, mobos and gpus or cpus you be better off with a used good computer to start with.
do not stuck in an upgrade cycle from hell - u been warned!