Working or otherwise ... buy 'em, quick check the hardware, dump the OS in favour of the latest Ubuntu distribution (which contains open source equivalents of a few thousand dollars' worth of software, including the ultra-pimp Compiz and beryl 3D user interfaces) print a few PDF user manuals, and you're rocking.
I have a relative I set up doing something similar -- he buys used computers, rips out the innards and puts them in a flat form factor, installs a Linux OS, Myth TV and some other media apps, and lo and behold you have a media server that can kick a $x,000 Dell or Gateway media system to the curb for a a fraction of the price. He gets the computers for usually $200 or less, spends $100 or less on new parts, software is free, then sells the systems for anywhere from $750 to $2,250 depending on configuration. Not a bad deal.
PS. Here's a look at Compiz: Link hidden: Login to view
PPS. Link hidden: Login to view
to see Compiz running a game of Quake across twenty-four monitors. Yum.
PPPS. Compiz=free with any purchase of Ubuntu, which is free itself.