That you mention "Windows Picture and Fax Viewer" makes me think that you
are more likely running XP than Win Me but what follows applies regardless
of the operating system you are using - you just need to replace "Image
Preview" by "Windows Picture and Fax Viewer".

Re-associate the file type(s) that has been hijacked by QuickTime it is
important to first unassociate QuickTime otherwise when QuickTime is next
run it will grab back the associations.  The QuickTime associations are
set via QuickTime's Edit | Preferences | QuickTime Preferences, open the
File Types tab and start unchecking, for example click the + alongside
Images - Still image files and uncheck away - in my case I only have
MacPaint, PICT and QuickTime image checked

To re-associate your scanned files, Control Panel | Folder Options | File
Types, browse to the file types involved.  Taking type JPG as an example.
If this was/is opening in QuickTIme, scroll down to and highlight
Extension JPG and either click the Restore button if present or if not
Change and select "Image Preview" from the applications offered.
Alternatively right click on a file for whose extension you want to alter
the default application and then select Open With and select File Preview
for the options offered and check the box "Always use this program to open
these files".