For Peale (and others who like slow machines for classics)

[Lilwolf]

This should run vintage well... 5 bucks

http://www.microcenter.com/single_product_results.phtml?product_id=0134173

[JoyMonkey]

Nice.

Another option for getting old slow PCs is to put an ad on CraigsList in their Wanted or Free Stuff sections - I did this last week and was over-run with people trying to get rid of their old PCs.

[SirPeale]

What's vintage?  Some new emulator?

[Buddabing]

RetroBox has cheap stuff too, you can get a PC with a 266-333 MHz processor, hard disk, CD-ROM, keyboard, mouse for less than $60 shipped. Not bad. Unfortunately, I can't tell whether or not they have AGP slots....

[ChadTower]

In most towns now you can't throw a computer in the trash.  Find out where people take dead PCs.  In my town, and lots of towns, it's a central recycling center like the Highway Dropoff.  Go there.  They'll usually let you take whatever you want so long as you take it whole and don't leave parts behind.  Take 3-4 machines that look of reasonable age (i.e. they have usb ports).  Most of them will work with a single component replacement, many still work but just got thrown out.  Usually they'll be around a low end pentium.  Between those machines, you'll certainly be able to assemble one good working machine with a few spare parts at the very least.  There's your mame machine...