MS Paint will allow you to crop pics, but I'm not sure if you can customize the ratio, i.e. instead of shrinking a pick that's 500x400 down to 100x100 MS Paint may force you to keep the ratio of 5-4, so when you select 100 the ratio will turn out 100x80.
I do have a few apps that will allow you to customize the radio, Ulead Gif Animator (Which is what I use to make gifs, also works on image frames), Photoshop, etc.
Or you can simply post the pic here (Or send it to myself) and I can bring it down for you. Whatever floats your boat...