You say you want to play Maniac Mansion on your Macintosh?
"But wait," I hear you saying "Maniac Mansion was never ported to the Macintosh..."
Don't let that pesky fact stop ya...
  1. Load up Day of the Tentacle (the sequel to Maniac Mansion)
  2. Have Bernard go in to Big Ed's room
  3. use computer (five times in a row)
You'll now be able to play Maniac Mansion in all its splendor.

(you can also give ScummVM a try)