Megatouch machines run from custom hardware to not-quite-a-pc. They can't run windows. The cabinet modification would be something akin to custom kick boxes in a car, lots of fiberglass work. Screen resolution would probably work, and if I'm remembering correctly, they use standard HDD's.
Megatouch would be a pretty poop choice. Better off putting together a kit bartop, especially considering what the Megatouch machines cost.