I believe this to be the NT driver. The trick (as I remember it WITHOUT HAVING TO RUN isa pnp) is to set the IRQ and I/O to the same as your onboard com2 ensure NT sees the com port, drop to BIOS, disable the Com port then turn off and insert the modem. Go back into NT add a modem from control panel, click Have disk and point NT at these Inf files.
Good luck. There are easer ways of doing it but as I now use an external USR modem and Linux I haven't bothered to work them out.