how do i insert a pic on top of my signature?

In the signature text box in your user cp, enter [ IMG ]http://url.of.your.image.jpg[ /img ]

For example:

[ IMG ]http://www.allforums.net/images/forums_logo.gif[ /IMG ]

Would give you the allforums logo in your sig.

Just delete the spaces between the brackets, and make them [/img] and [img].