Well, if you have a little bit of the plug sticking out you can try pliers, but I don't think you do if you're asking us.
Unfortunately, I've thought of several methods, but all of them involve damage to, at the very least, the port in question. Worse, the motherboard or yourself. I mean, technically yes, you COULD get it out, and you might not damage the system, but I promise, the jack won't work properly again (at the least, keeping it plugged in would be problematic, as the only real way to remove the thing would be to widen the hole.
To be honest, I'd be on the safe side and purchase a new sound card (it's not too expensive; a good one can run about $30-$50, depending on whether you're using Surround Sound or not) and a new microphone.