I thought i might add my $0.02 worth

When upgrading a brand name p/c you will find that the operating system wont work with other mother boards. it fails to recognize the system and shuts down the setup. The OEM licensing is designed to identify the mother board to prevent piracy. on another note a few of the higher end video cards need a lot of power from the power supply a 9800 pro ati wont even boot up with a generic power supply from HP unless you ordered something over 300 watts. i was amazed at how much current they used a few people with the ati cards found out the hard way just how much power is needed this is the ATI 9800