Getting a Driver for LT Win modem is easy Trying to get it to the right COM port is hard
On systems with 2 built-in com ports and an internal modem, the only safe com port you can use is one that is not an even or odd number as is the modem. So if your modem is com1 you cannot use com3, if its com2 you can not use com4.
Further, if your mouse is connected to a serial port it works as above with the modem. If the mouse is on com1 then using the com3 will cause problems, if its on com2 using the com4 will cause problems.