This is the official site for the UK borders agency. Bear in mind that the rules have just changed in the UK for non-EU nationals. There is now a points-based system for people who wish to work in the UK. If you're just wanting to study at a UK university though, you shouldn't be affected, but apparently they're considering changing the rules for students next year (you might need to demonstrate that you have enough money to cover your living costs before you'll be granted a visa, for example, and that figure will probably be a lot of money).
There is also this website, which is specifically concerned with the interests of international students in the UK.