I just installed a 2.8 prescott chip, running windows 2k pro. Windows says I have a acpi multiprocessor system. And task manager shows 2 cpu usage boxes. Any ideas why?

You have 'hyperthreading' enabled on the processor. That is a feature of the processor, and if you have application programs which can make use of the feature, it will improve their performance.

http://www.intel.com/technology/hyperthread/

I wasn't aware that it would show as another cpu though. Some games have small graphical glitches unless I set it for cpu0 only.

heh heh.......

Thought you'd been given a bonus birthday present, didn't you?

hehe...

I don't claim to be an Intel Expert, but isn't Hyperthreading special because the chip has dual execution units, so there's two execution units feeding data to the core, thus making the system seem like a dual system?

In a nutshell, yes- you've got it Alex.

A Hyperthreaded CPU implements 2 logical "Architectural States" which share the same physical core; the OS will see/identify each logical portion as a separate processor. In fact, if you have an OS which supports two (or more) physical processors, and each of those processors were hyperthreading, the OS would report that you have 4 (or more) processors.