I have no idea what your skill level is. But even if you are an experienced photoshopper the GIMP can take a little time to learn.
Paint.NET is the actual name of another *great* and free graphics program that has a subset of all the gizmos the GIMP has but is still quite powerful. I used it here on FR for a long time before I got the GIMP up and running. It is really good for editing pics and adding captions and text, resizing, etc. Check it out, too. A lot of the things you see on FR can be done in Paint.NET.