I'm a pretty introverted dude, but I never really had too much trouble meeting new people... whether it be at work or college. I am lucky in that I still have many of the friends I've had since 11th grade (only problem is that lately they have been extremely reclusive). It takes me a bit of time to open up to people, but the best way to do it is to go along when you are invited to a social event, or attempt to make conversation. When I started my job at NGC, 5 years ago, I was afraid since I didn't know anybody. But I met quite a few people just from talking to them a lot and getting to know them. When they invited me along places, initially I hesitated, since they were a bit of a drive away from me and liked going to more "meat market" type bars. Then I decided "what the hell?", especially after my core group of friends got more and more reclusive.
Ended up having a lot of fun hanging out with the work kids, since they were a bit more proactive and easygoing. Just, if people invite you out, take them up on the offer.. or throw your own party/gathering and invite people. Just keep working at it, and eventually you will find people you just "click" with and are comfortable opening up to.