No problem.
If you've already made a banner in Paint Shop Pro or something similar, you need to upload the file to a server such as Photobucket or ImageShack (both free), then get the URL address for the file and insert it between [img] and [/img] brackets in your signature box in your profile.
If you haven't got a banner made, then there are loads of really talented banner makers on the Forum ...... I'm sure one of them would help you out.