Check out
www.scummvm.org for an emulator that lets you play the Sierra and LucasArts games (and many others) on basically any platform -- I play them on my phone.
Also, updated versions of Monkey Island 1&2 have recently been released. I played part of #1 and it was well done, true to the original but with nice higher rez graphics and voice acting (lead character done by the same voice actor from Monkey Island 3).