I installed TMI on a second computer; actually a Virtual Machine running Windows Vista (host OS Mac OS X). After dropping the graphics level down to 6, the game plays acceptably. However, there was a weird graphics glitch during the cut scene between the intro (on the boats) and when Guybrush washes up on Flotsam Island. I've attached a screen shot; any idea what would cause this?
I did let TMI install all the DirectX drivers it wanted to.