Int 61 Fn 0008  - Banyan Vines - Intercept Vines 25th-line Messages At Lo  [N]

   AX = 0008h
   BX = 0003h
   DS:DX -> request block

Return: AX = status
       0000h successful
       0001h network software not installed or incompatible

Notes: message handler should not call BIOS or DOS functions, and should
     either call next handler or simply return
   to stop intercepting messages, set prev and next request blocks to
     point at each other

See Also: AX=0008h/BX=0002h

Format of request block:
Offset Size    Description
 00h   DWORD   pointer to user-written message handler
 04h   DWORD   pointer to next request block (filled in by VINES)
 08h   DWORD   pointer to previous request block (filled in by VINES)
 0Ch   DWORD   pointer to message storage area (filled by VINES) (see below)

Format of message storage area:
Offset Size    Description
 00h 16 BYTEs  IPC port of message sender (see AX=0001h#"Sosock")
 10h   BYTE    message flags
 11h   WORD    reserved
 13h   BYTE    length of message
 14h 80 BYTEs  message text