INT 15 - DESQview/X 1.02 - DVDOS4GX.DVR - ???
        AX = BFDEh
        BX = 0005h
        CX = new value for ???
Return: BX = 0000h (success)
        AX = old value of ???
        DS:SI -> ??? (if AX nonzero on return)
        ES:DI -> ??? (if AX zero on return)
Note:   called by DOS4GW.EXE