For good looking sigs you generaly (sp) need to download a editing program such as Gimp or Photoshop. If you weren't very serious in doing this just download Gimp because Photoshop cost a couple hundred of dollars. Then you might want to check out a graphics site like Linky to get some ideas of how to do them or just mess around for a while. It is hard I am just now starting to get a little good if you don't want to spend a whole bunch of time and/or effort just make a new topic for a request. Remember the more specific the better. I would make you one but I have been very busy lately and I don't want another thing to do. sorry hopefully this helps, if it doesn't there are a lot of great a/v guys on this board who could help.
If you just register on the link that huskerfan provided, start this exact thread on that board and i garuntee you will get a very specific answer. They know their stuff over there....