|Generally that error is RAM related. You need to research the STOP code error to help narrow it down.|
But before going any further, did you look into the driver issue before you dove into this "downgrade"? The problem is, there may not be any XP drivers for your new hardware. The audio & network are the two that normally are the problem devices. See if you can locate all the XP drivers (chipset, video, audio, network, etc) before continuing with the installation.