Any level, eh?
My dad did it, he did a degree and then later a master's degree, the exam kind rather than the research kind.
If you're doing it whilst working full time it takes longer than your ordinary uni course.
The distance part works, or at least worked, by them sending you a pile of books and I think attending a lecture every so often, every few months. And you have exams which are sat in some Novotel-type place near to you.
During dad's master's, they were encouraging some kind of internet conferencing stuff as well, I should imagine there will be more of this nowadays.
Edit: I say 'if you're doing whilst working full time it takes longer', well, that's obvious but I don't know if there's an option to do it over a shorter time if you're able to study more of the day.