I have a soft spot for PentiumD's (used an off the shelf eMachines tower powered by one as my main computer for awhile before I got the Mac Pro, and it worked decently, and was relatively fast under XP and even Mac OS X Tiger (it was my first Hackintosh experience, and the chipset happened to be almost identical to the MacBooks and MacMinis of the time, which made it super easy)), so if you find you don't need/want that particular CPU, I'd take it (and its heatsink) from you.

Anyway, your work with retrobright (aka Yellow Be Gone!) is impressive!

c