First make sure that your motherboard has the latest BIOS, if it doesn?t then flash it to the latest version from the manufacturer?s website.
You can then install the dual core processor. Upon the first boot with the dual core processor installed, windows ?should? dynamically update the HAL to a multiprocessor HAL, over the current uni processor HAL. If it doesn?t update automatically you can update the HAL manually, but this shouldn?t be necessary.