Filter: Mac's Remove White
Author's site: http://members.xoom.com/markmclaren/
Versions: Photoshop 5.5, 6, and 7

To isntall:
1.  Close Photoshop, if open
2.  Unzip the filter to Program Files\Adobe\Photoshop x\Plug-Ins\Filters directory.
3.  Start Photoshop - the new filter will be listed under the Filter menu option.