Very very sorry for the late response! I went outside soon before you posted, so I couldn't reply. Basically to upload background images you need to upload the image to an album first - THEN put the link in the background picture section. this is what mine looks like atm:
once you upload an image you need to copy this link (NOT BBcode) to the background picture section:
You can mess around a bit with sizes and cropping in any simple program like pain to make your profile perfect :D