How to sharpen a picture quality?

Ok, I just got back from a concert and I took a bunch of pictures. The camera I had is 8.1 megapixels, so its a really good camera. But where I was standing in the floor in a crowd of thousands of people, it was hard to get a clear, still shot. Many pictures of mine are flawless, but most just have a small blur that I think I might can get out with something to sharpen the image. So, is there somehow I can do it with paint, or what free program can I get to help out? Thanks.

Any generic paint program that isn't MS Paint has a sharpening feature. Generally, these work best on text and very poorly on anything else.

GIMP should do this GIMP - for Windows