Those keypads are not rigged to standard keyboard controllers and is thus not controlled by standard keyboard drivers.
I am pretty sure the manufacturer writes their own software. From what I read, many times they pick Windows because they have these braindead programmers coming out of college now who are used to win32.
On one hand, Linux would be a good choice for these boxes, because you could strip it down completely and tweak the kernel. OTOH, Diebold would have to release the source of their custom kernel, and this is something that would turn off a heck of a lot of managers, and would scare off many clients.
No, BSD would be the better choice.
But Windows lets you do all the pretty graphics and talking sounds and stuff easier than BSD would. All of which is utterly useless and just pisses me off. IMHO bank machines should be spartan and reliable, something Windows is not. OS/2 fit the bill nicely.