Acting classes may be a good idea. Even if you learn nothing in terms of conversational skills, body language, etc, at the very least you'll gain more confidence in having others listen to your voice.
But you shouldn't need to learn how to 'act' in order to have a conversation with someone. You have to learn to be yourself. (Don't you HATE it when people say that!?

) Whatever you are constantly thinking about is sure to become things that you're constantly talking about. That is why it's hard when you're going through depression, or any type of problem, as it is hard not to talk about things that are on your mind. And we all know that there is a limit to how much 'problem-talk' we can all handle.
Have you ever noticed how most people who have conversations always have something in common? For example, they work together, study together, or have a common interest. This is what people always revert to when they have nothing else to talk about.
In my first full-time job, this seemed to be the case. We were all different ages, had different backgrounds, family life, beliefs, you name it. So in the beginning, all we ever talked about was work. GROAN!
So I did the whole asking question thing, to ease my boredom a little. It was also interesting at the start, coz the people who never talked much were often REALLY boring to listen to. So I quickly learnt the art of interjecting without being rude. Some ways I'd do this was...well, first I'd make sure I was actually LISTENING to them. If you don't, you will end up being rude, and they'll get upset coz they'll know you haven't been listening. (But remember, even the 'boring' person isn't enjoying it either...noone wants to talk when they know noone's listening).
Sorry guys, if this is all jumbly diddly dobbly...I'm trying to explain myself, but there are so many questions I'm trying to comment on all at once! Bare with me!
So...what did I do to interject...hmmm....as I said, I'd listen. And in order to understand people, I usually picture what they're talking about, and also try to relate it to similar things in my past. Have you guys ever done word association? Where someone says a word, and you say the first thing that comes into your mind. Well, I constantly do a similar version of this in my head. If someone mentions, say...coffee...I'll think of all the funny, interesting, and/or factual things I've heard/read/seen/experienced with coffee.
That's one way of interjecting; verbalising your associative thoughts; and it's good because it shows you're listening and/or gives everyone a chance to divert the conversation.
Another thing I've found helpful, is to use other people's stories. That way, you're not talking about yourself, so you're not as anxious about people finding out about your problems, or thinking you're stupid or whatever. A good way to come up with these is...to think of times you've spent with other people where they've done stupid things; read newspapers, magazines, books, the internet...there are always millions of interesting stories there.
Hmmm...I haven't really mentioned how to go about actually getting up the courage to open your mouth in the first place, have I? Well; I've found that out of all the people I've talked to, often it's the quietest ones who have the best stories! Usually the louder people just let them remain that way, as they assume that's what they'd rather do. So the more the quiet people start to comment on things, the more everyone else will begin to tune in as they speak.
Sorry for such a long, boring babble! I'll finish with this...talking is usually left to the loudest, blabbiest people...like me! BLAAAAAAAAHHHHH.
And by comparing your posts to mine, I know you have a multitude of things MUCH better than I ever do to share with the world. Please save the ears of the world and drown us out!
Luv u all!