Int 10 Fn 80  U - Video - Desqview 2.0x Only - Internal - Set ??? Handler  [Q]

   AH = 80h
   DX = 4456h ('DV')
   ES:DI -> FAR subroutine to be called on ???

Return: DS = segment of DESQview data structure for video buffer

Note:  this function is probably meant for internal use only, due to the magic
     value required in DX
   the subroutine seems to be called when the DESQview menu is accessed;
     on entry, AL = 03h or 04h