Do you have a pic already on the web?

If so, just

go to user cp at top right of screen

go to edit profile

scroll down to signature

copy the address of the pic and paste it in the sig space

put [/IMG] at the end and [IMG] at the beginning

If the pic is not on the web, try uploading it on something like image station. Put the pic in an album and copy the address, as noted above. Try to keep the pic file under 20 or 30, so it doesn't take up too much space.

Hope this helps