Format of FGDRIVER MOUSEBUT variable pointer record:
Offset	Size	Description	)
 00h	WORD	segment of WORD buffer for press/release count
 02h	WORD	offset of WORD buffer for press/release count
 04h	WORD	segment of WORD buffer for screen space col of last press/rls
 06h	WORD	offset of WORD buffer for screen space col of last press/rels
 08h	WORD	segment of WORD buffer for screen space row of last press/rls
 0Ah	WORD	offset of WORD buffer for screen space row of last press/rls