I'm the same kind of introvert people than you. Here are some advices I'm using myself to be more talkative.
In non professional situation, you can ask questions about the others.
This way you don't have to talk to much but you will be active in the conversation.
Try to find what are interesting for the other, and then ask questions. If you speak with some enthusiast and talkative person, he will drive the conversation.
If you listen, then you will learn a lot about the person and a friendly feeling will be set between you.
Don't hesitate to joke (but nothing offending), smile and use a pinch of self derision or non-sense: try to look not too serious or boring.
In professional situation, you need enough self confidence to speak with authority about important matter. Being a silent person can be an advantage: people might listen to you more carefully (silent people are considered as wise in the collective perception of things). Use the advices from JB King in order to avoid confrontation.
If you are afraid of talking in front of other, you can try to blank out the audience in your mind at the beginning: imagine that you are alone in your own room. Once you start to feel good (or at least a bit better) then re-connect with the audience. Use the feedback sent by their faces and body to adapt your speech and behavior: are they bored, convinced, amused, interested ?
To limit the stress you need to breath deeply and slowly, and to focus on what you are doing, not on what the others are thinking of you.
Another tip to avoid running out of question, is to read/listen/watch news from the world about different topics. I have a google news page pre-configured with differents topic (politics, international, science, ...).
I scan this page a few time a day (beware not to waste time on useless stuff) and this way I'm able to open discussions about these news. I use different kind of news with different kind of people (computer/technical/gadget stuff with my colleagues, politic with friends, ...) You don't need to be an expert, it is just a way to have many entry points to conversations.