I was obcessed with the A500 once. If you wanna build an overexpanded one, get the CPU adaptor slot from Mikronic. Some years ago they made an adaptor that allows you to use A2000 CPU cards. As for PCI adaptors don't remember any for the A500, but maybe there was one for the A2000, so you'd have to use the CPU slot adaptor for the A2000 and then the PCI adaptor (but I'm not sure if anything for the A2000 existed, or if it'd work this way).
You'll of course need a tower to put the A500 motherboard.
Ok, what I should've told you in the begining before you got excited, was that the A2000 is more limited in capabilities than an A3/4000, and you'll spend lots and lots of cash with wich you could buy much better stuff for say an A1200.
