Mustek 1200UB Scanner & Windows XP

Having installed Windows XP and forced the Windows 2000 driver for my Mustek 1200UB scanner (USB device), using Administrator logon and following the instructions at http://www.computing.net/windowsxp/wwwboard/forum/1597.html I find I am the only one with the following problem. Regardless of which photo software package I use (tried PaintShop Pro 7 & PhotoImpact 6), my scans are only 50% of the original page width (and then stretched to fill page). I also have a Philips Vesta pro webcam (only other USB device fitted) which I uninstalled prior to installing scanner driver, but with or without this other device installed, the result is the same. I then removed the Twain and Twunk files (which XP didn't like) prior to another attempt, but after completing installation - no change. Is something getting left behind from my other USB device which is hindering my scanner installation ? Or am I barking up the wrong tree ?