Well, you could use a picture editing software, but the easiest would be if you had a picture of a certain size, preferably bigger than the largest allowed sig. size. Upload it to "tinypic.com", where you can choose which size you want. There you have different alteratives, standard forum avatar size, thumbnail size etc. try and see~
They host pictures so you'll just have to link it when changing your signature.
ahh, ok thank you.
Np, it's simple to use, so I don't think you'll have any problems with it, but if you do, just ask~