Whilst researching my thin client to figure out how to get it to boot from the IDE/ATA interface, I discovered something incredible that those wonderful hackers out there have been doing for quite some time.
They have been simply yanking motherboards out of old computers and replacing the power supply with a small 12 volt regulator board, the hard drive with a compact flash adapter (see link above) and a passive backplane for some add-on boards and basically creating their own embedded computers at 25% of the weight and volume and a 50% leap in performance.
If you can replace the hard drive (heaviest thing in most old machines) and the power supply (stepdown transformer beast like a concrete brick) you're just left with what is essentially an embedded x86 PC you can stick anywhere. Suddenly I'm feeling queasy about those old machines I've been stripping for parts and chucking. I'm thinking that motherboard would have been just dandy with a little work.
The other way you can cheat the architecture is to buy a single ISA card adapter that allows you to stack a couple PCMCIA cards together in one slot for networking, serial ports, USB, etc.
This also gives you much broader scavenging options when TSHTF. I was at the scrapyard a couple of months ago and I saw a stack of discarded Pentiums that nearly reached the moon. They were the smaller kind of board design, too.
With a bit of ingenuity you could get your basic hardware costs down for Vault OS to no more than $1.00 a terminal in most cases.