INT 21 - Gravis UltraSound - MegaEm/MEGA_EM - INSTALLATION CHECK                
	AX = FD12h
	BX = 3457h
Return: AX = 5678h if installed
	BX = 1235h if v1.x or v2.x installed
	    CL = interrupt vector used by MegaEm (default 81h)
	BX = 1237h if v3.x installed
	    CL = interrupt vector used by MegaEm (default 81h)
	    DX = version number
Program: MegaEm is a protected-mode SoundBlasterA common sound card developed by Creative Labs., SoundCanvas, and MT-32
	  emulator for the Gravis UltraSound
SeeAlso: INT 2F/AX=CD00h/BX=464Fh,INT 7E/AX=00FEh"SBOS",INT 81/AX=0200h