The best deal in this freestuff is a i5 quad core with 8G and W7. I had to play with it a bit to get it to post - basically needed the ram reseated and a couple of minor other things. BUT.. I don't have the password to get into Windoze, so I'll probably be reinstalling/upgrading Windoze to Pro from the present homely edition..
The next-in-usefullness box has a AMD AthlonII-X2 in it, 6G ram, but no hard drive. Assuminf nothing in the mobo area is fried, a hard drive and op system will get that one up and running. The only caveat is that it has a mobo with the nVidia chipset of the vintage that melts.. shouldn't be a problen if some overclocking nut doesn't get a hold of it.
The third box is a single core with WinXP on it, very dirty inside and full of crapware. It had a bad stick of ram (that someone stuck in it and it was even the wrong 'speed' (133 mhz ram doesn't clock well on a 200 mhz bus). It also had a bios password on it for some strange reason but I removed the 2032 for long enough to make a sandwich and in short order there was no more password. Took forever to boot, and after snooping through what was left behind on the hard drive I think I figured out why there was a bios password... The hd is only 200 gig and as such is maybe useful as a second drive somewhere but the rest of the stuff...
The HP printer/scanner thingie I haven't looked at yet because, as you said, a power supply is an easy fix. I didn't look to ssee if there were ink cartridges in it, but the print head could be all clogged up if it wasn't used recently, ink jets do that.(It does however use a different connector on the power input than anything I have hanging around, so it probably will necessitate a trip to the Bay of E.
And on that note, I've killed the entire night and I probably should think about someplace more horizontal.