Maybe this will be helpful:
http://lucasarts.vintagegaming.org
The best version is the "Enhanced" version which is included in the Classic Adventures and also may be in one of the Kixx or Lucasarts rereleases. It is still only 16 colors though. The version included with DOTT is the standard version, you don't want to play that one unless you have to. If you really want to, just rename "maniac.ovl" to "maniac.exe" and run it.
There is no FM Towns version of Maniac Mansion.
