Windows 2000 recognizes dual processors just fine when upgrading from NT 4.0. But a "clean install" of W2K sees only one processor. This cuts your PC's performance. In NT, the Uptomp.exe utility adds multiprocessor support. But in Windows 2000, you fix the problem using Device Manager. Heres what i dug up
Step 1. Log on to the W2K machine with Administrator privileges.
Step 2. Click Start, Settings, Control Panel, and open the System applet.
Step 3. Click the Hardware tab, then click Device Manager. Expand the Computer branch. You see a line describing a single-processor PC.
Step 4. Double-click this line, then click the Driver tab, then Update Driver, Next. Display the list of known drivers, then click Next and click "Show all hardware of this device class." Select the same type of computer you have, but choose a "multiprocessor PC." Click Next, then Finish, and you're done.
Microsoft says W2K also sometimes does not recognize dual processors when it's installed over Windows 98 across a network. The same steps may help you in that case.
Microsoft cautions that you shouldn't perform this change to support a new BIOS. For example, if you upgrade an older BIOS to a new one that supports the ACPI (Advanced Configuration and Power Interface), you must reinstall Windows 2000 as an upgrade.
For the correct procedure, read about dual processors at search.microsoft.com/us/default.asp. Search for Q237556 and Q234558.