
No, but some OS's ( COHERENT , etc ) are able to drive one of the ports in
polled mode without using the IRQ. In your example, after accessing the
modem, the mouse won't work until you reboot, because the IRQ is used by
the modem.


Yes, you can change the IRQ's for com3/4, but it depends on your other
hardware. com1 uses IRQ4, com2 IRQ3.  If you have only one printerport 
( IRQ7 ), you can change com3 to IRQ5 ( normally 2nd printer ). For com4,
you can assign IRQ2, if its free. As far as I know, no other IRQ can be
used until your I/O-card is 16bit and caould access IRQ's > 8.

Michael