Phill wrote on 18.04.12 at 23:14:01:

Does that interrupt stay active or does it automatically close when a mouse event has occured?

It will stay active, but, as mentioned above, the game will always have to poll the mouse state. There will be no automatic mouse report interrupts.
Keys will still be reported automatically via an interrupt.

In the game's ikbd routine, look for the place where the routine checks for an $f7 byte. This is the header byte for an absolute mouse packet. The game should set a flag somewhere to remember that. The next five interrupts following will report the absolute mouse packet proper, byte by byte.