I've not read all the posts. But OP, I used to be like you. Still kind of am around big groups of people.
Here's what I did.
Step 1: Join a forum of your interests - You're on OcUK forums. Step one complete.
(Could always join more if it helps, I used to be part of Warrior Nation which is a multi gaming clan)
Step 2: Get a messenger client for a specific purpose, for example Skype or Xfire.
Step 3: (Basing this on gaming now) Start playing games more frequently with a set group of people. I currently play DotA with a group of people and we're always talking.
Step 4: By now you'll be discussing things about the game, tactics, etc.
Step 5: When you feel comfortable, now this is the hardest step, call them. On Skype, Xfire, whatever you use. Make it a group conversation, at first it'll be awkward, believe me. I sat there in a group call saying nothing, just listening, because I didn't know what to say. I thought "What if they don't care what I have to say?" "What if they think I'm stupid?" "What if they just get annoyed by me?"
They won't. They'll get to know what you're like just from typing. You'll be able to speak to them no problem after a week or so. The first week IS daunting, but you'll be fine.

This will boost your confidence with talking to people IRL two-fold.
Step 6: Speak to people in real life. Don't necessarily strike up a conversation, but just speak back to them. Imagine you're in your room, on skype, talking to your friends that you play games with. They don't judge you, why will this person?
Step 7: Use your interests in conversations to start them. "Hey, just wondering, do you happen to play <Insert game>?" if they say "No" just talk to them about it, briefly, see if they are interested. If they are, try hook them up with a trial or something, if not then don't mention it again unless they do.
Now, that isn't the most glamorous looking list. Alter it as you like, but this is what worked for me.