How to get Vista to see both processors after motherboard upgrade?

When I go to Device Manager and expand the "Computer" node, I see:

Advanced Configuration and Power Interface (APCI) PC

But think this is the wrong driver for my motherboard, which is NOT what was
in the case when I first installed Vista (original mobo was single proc). I
upgraded to a dual processor motherboard and now Vista does not see both
processors (Control Panel > System shows only one processor, and Task
Manager shows only one processor).

From what I've read, the driver under the "Computer" node needs to be
upgraded to a multiprocessor driver.

I don't want to reinstall Vista, and I don't know where to get the correct
driver. I've tried using the chipset drivers for the new motherboard
(Compaq Evo Professional Workstation - dual Xeon) but that was no help.

How do I get Vista to see both processors after this motherboard upgrade?
Do I need to update that "Computer" driver in Device Manager? If so, where
do I get the right driver?

Thanks in advance.