Today I was having exactly the same problem with my scanner. I didn't find anything helpful on the Net. All I found was this post. But no solution of the problem. So I had to find it out on my own. As you already guessed it, the spring works as a tensioner for the belt. I inserted the spring about an inch away from where the belt is attached to the scan. First I had to open the scanner, then I removed the screw and the cog wheel which is located opposite to the motor that moves the scan. Then I removed the rod that works as a guiding rail for the scan to move back and forth. Now I turned the scan over, so that I had free access to the belt. I inserted the spring in a vertical direction, so that the belt is wrapped around the spring. Think of the Greek letter omega - that's what it should look like, when the spring is inserted correctly. Now you can put all parts back together, clean the glas pane and you're done. Maybe it would have been more helpful to you, if I'd been able to upload a photograph. But I hope you'll get a clue how to do it from my verbal description anyway.
Regards,
Crocodile Dundee
Crocodile Dundee, February 2008
