The last driver released for the Mustek 1200 UB Plus
was for Windows 98 / ME / 2000 / XP.
There have been no new drivers released since then. See this:http://www.mustek.com/mustek/supportdrivers.php
The only way you can use that scanner on Windows 7 is by installing trial version of VueScan from here: http://www.hamrick.com/
If you want to keep using VueScan after 30 days trial period, it will cost you $39.95 for a Serial Number.
So your choice is clear: you either buy VueScan or buy a new scanner.