It's illegal to run OSX on non-apple hardware? Or just illegal to make homemade drivers?

I would think Apple would want to make their OS available for people with non-apple hardware, so they could sell more software. They could also make it easier to run windows on apple hardware, since apple makes nicer laptops than most if not all non-apple notebooks.

If I wanted to, could I reformat my MacBook's hard drive, give it a windows file system, and then install Vista as the only OS? (not that I would want to do this)

edit: just as an aside, i recently conducted a survey of students at my law school on what OS they use on the laptops they bring to class, and two out of the 200 or so respondents chose option (c) which was "my laptop runs on an OS other than a Windows or Mac OS." I should go find out who these two people were, and see if they were just lying or if they actual use linux (or whatever) laptops for school.