Note that the subservice number must go into AX, not AH or AL
individually.


Service 33H, subservice 0:  Reset Mouse and Get Status

   Returns 0 in AX if there is an error, e.g. if no mouse is present.


Service 33H, subservice 1:  Show Mouse Pointer

   The mouse pointer will appear at the center of the screen.


Service 33H, subservice 5:  Get Button Press Information

   The information will be returned in AX, with bits 0, 1 and 2
   indicating information on the left, middle and right buttons,
   respectively (a value of 1 means the button is down, 0 means
   up).


Service 33H, subservice 3:  Get Mouse Position

   The current mouse position will be returned in registers CX and 
   DX.  These will be pixel positions for a "virtual screen" which
   has 8*25 = 200 pixels vertically and 8*80 = 460 pixels horizontally.
   So, to translate this to row and column numbers, use div 8.