Just another bit of reassurance for everyone feeling that some of the replies here are quite hostile.
If you don't feel comfortable doing some things that are offered in Freshers Week, don't feel pressured into doing them. Whether it's because you don't drink, you don't like big crowds, you don't like loud music or whatever, if there is an event on that you know you don't want to go to, don't feel obliged to because you "won't make friends" otherwise.
Staying at home some nights (or even every night!) doesn't make you anti-social, or a loner. If you wander through Halls you'll find other people who didn't go to whatever events are on, because, like you, they didn't want to, or because they got too drunk pre-drinking and passed out, or because they had so much fun pre-drinking that they're still there. Most of these people will be happy to see you and will welcome you joining them with whatever they're doing!
I was worried about Freshers - I'm at Warwick so it was a fortnight - because whilst I drink, I'd never had more than a couple before, and I felt very uncomfortable around drunk people, esepcially strangers. I also hate clubbing and crowds and pretty much any "event" that the University had organised for Freshers.
I was lucky enough to have a quiet flat who stayed in most nights as well, so we played "tame" drinking games in our flat, or just chatted, and we bonded really well because of it.
I get that a lot of the time it's not "oh but I don't want to drink" that puts you off Freshers, it's the fact that most events seem to be geared around alcohol, you may have faced aggression over not drinking before and aren't sure what to expect at Uni, but also, you simply don't like being around drunk people. There's a difference between that and "not liking people who drink" or looking down on those people.
What I'm trying to say is, don't let people tell you that by not getting involved in events including alcohol you are sticking your nose in the air and considering yourself better than drinkers. Don't let people tell you that you have to put yourself out there and go ouside your comfort zone in order to make friends. Yes, it's good if you do get involved in events, and if you push your limits a bit, but you certainly don't have to do so. Staying in your room for the first week isn't to be advised, but staying in your flat, or your building, because that's what you're comfortable with, is nothing to be ashamed of.
Sorry for the essay, I just wanted to offer the advice that I know I would need if I'd just read some of these comments a month before starting Uni for the first time!