As far as making the signature (the banner) you can do just about anything. Make a 400X100 pixel image in Photoshop, customize it, and save it as a JPG, GIF, or PNG.
Now you need to upload it to an image host, I recommend
TinyPic.com. So once you upload it, there will be a few text fields. Copy the one that looks like this - [IMG ]http://i25.tinypic.com/210lf28.jpg[/ IMG].
Then you need to come to the forum, goto Profile > Modify Profile > Forum Profile. If you scroll down there should be a text field called Signiture. Paste the code you copied earlier in there. Hit save and your done.