The quality of ISA prototyping boards varies widely.

I was seriously disappointed with the otherwise excellent boards offered by Vector, specifically, those with a solid Vcc plane on one side an GND on the other, when I discovered that the apparent fool who laid the board out had staggered the contacts at the isa-bus connection such that it couldn't be used with their "staking board" for setting pins, and a few other reasons. Oddly enough, the boards without the ground/power planes were not "messed up" in the same way.

The typical PC's ISA bus is pretty noisy on the power and gnd lines, and that affects everything that uses power and ground. PC power supplies, generally speaking, are far too noisy for anything other than crude 5-volt digital logic. The noise on +5 and GND, once a load is applied, will probably surprise you!

For that reason, you will probably want to use ferrites to filter the supply paths. Those ground and power planes make that easy and make bypassing the supply to gnd easy as well.

RE