I HATED my first few weeks at uni. I knew absolutely no one in my course and missed lunchtimes my friends so much. Each lecture/tutorial I sat next to someone new, introduced myself etc etc but when it was over everyone seemed to go off in their newly founded groups and I'd be forced to wander off pretending to be busy. This happened regularly until I hardened up and one day bought lunch and just sat with some girls that looked familiar. They were both as lonerish as me and we're now good friends
You'll have a lot more in common with the people in your course than your friends at school because you've CHOSEN to do that course and often have similar interests. I suggest joining as many clubs as you can and getting involved in O-week crap because you will meet a lot of people. And even if you don't see them again for a few weeks, it's still nice seeing a familiar face around (and you can score a free lunch or something at these events). I agree with what other posters have said about people from your school, even if you never really spoke to them, they'll be very happy to talk to you as they don't know many people either!
Instead of going into second year uni I transferred courses..2 weeks into the semester...and had a lot of trouble meeting people as everyone already had their 'groups'. But you'll notice everyone's very friendly at uni (no 'popular' kids or whatever shit people stir at school) and once you've built up the courage to start some smalltalk you'll meet some awesome people.