Int 21 Fn 25  - DOS 1+ - Set Interrupt Vector                              [D]

   AH = 25h
   AL = interrupt number
   DS:DX -> new interrupt handler

Notes: this function is preferred over direct modification of the interrupt
     vector table
   some DOS extenders place an API on this function, as it is not
     directly meaningful in protected mode
   under DR-DOS 5.0+, this function does not use any of the DOS-internal
     stacks and may thus be called at any time
   Novell NetWare (except the new DOS Requester) monitors the offset of
     any INT 24 set, and if equal to the value at startup, substitutes
     its own handler to allow handling of network errors; this introduces
     the potential bug that any program whose INT 24 handler offset
     happens to be the same as COMMAND.COM's will not have its INT 24
     handler installed

See Also: AX=2501h,AH=35h