DOS is probably easier as you have direct acces to the parallel port, get hold of an old computer from the IT department and install FreeDOS.
You can do it with XP, you need Visual Basic an an ActivX control, oh on second thoughts try FreeBASIC, it's fairly easy to use.
I'm not meaning to sound rude but why are you teaching this in Geography/History? I though this would be the sort of thing taught in Design and technology.
To be honest I wouldn't use a PC at all, I'd use a PIC, PLC or even an elaborate array of CMOS gates rather than a PC.