Here is a 96 Piece Security Bit Set that will help you crack the case on that sucker. Once inside, most microwave turntable motors are fairly simple to remove. I've heard that people go around scrounging them out of the trash because they're slow RPM motors that take 120v. Perfect for your disco ball or other slow rotating needs.
There are some security screws that protect the microwave from opening by everyone. The screwdrivers that open this class of screws are sold on any tool store like harborfreight.c