In April of 1998, I purchased a couple of surplus Epson IM-403 computers, used as the brains of a retail cash register. When I bought these from Timeline, Inc., I figured I was getting your typical surplus; some junked-out piece of hardware that had seen more than its share of abuse. Wrong! These were brand new, in factory cartons, ready for installation. Each rugged metal chassis houses a beautiful little 486SX-33 system with IDE and floppy controllers, four serial ports, one parallel port, built-in VGA, an empty 72-pin SIMM socket for memory expansion, and an empty 16-bit ISA slot! Not bad for $99 each.
Converting this baby into a working PC, complete with DOS 6.2, took several steps, none of them extreme for an accomplished hacker. In fact, except for one little episode with an I/O card, you don't even need a soldering iron. The conversion job requires the following steps:
1. Adding a keyboard and monitor
2. Adding memory
3. Adding an I/O card
4. Adding a floppy drive
5. Adding a hard drive
6. Loading DOS
The converted IM-403 makes a great DOS platform, and sits on my robot workbench right now. It's small enough and uses so little power (0.5 amps at 24 VDC) that it would probably work fine in a large robot.
Note that these pages only present a summary of the entire process, though it should be enough info for you to do the hack. For the full skinny, plus lots of pictures, check out the article I did for the July 1998 issue (I think!) of Nuts & Volts magazine.