In Windows 2000 (and above), to upgrade to multiprocessor, just open the Device Manager, under the Computer information, you should see ACPI uniprocessor.
Right click on this and tell it to update driver.
Click on the Install from a list or specified location.
On the next screen, click to choose the driver from a list.
The next screen should list the ACPI Uniprocessor kernel as well as ACPI Multiprocessor kernel.
Pick the Multi processor kernel and reboot when prompted.
After the reboot, you should have a multi processor machine.
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