The PC has support for up to four COM ports, so your internal modem
can probably configured for COM3 or COM4. COM3 and COM4 normally
share IRQs with COM1 and COM2, but if your modem and communication
program support it, try using a different IRQ (IRQ 5 is a fairly
good bet).
If your modem or communications software doesn't support additional
IRQs, then set them for COM4 which shares IRQ 3 with COM2 rather
than using COM3 which will conflict with your mouse on COM1.
Clear?
-- Doug