Over time I have often had problems installing this model modem, and judging by forums and newsgroups I am not alone. I recently had occasion to install this on a number of different systems and have found a method that seems to work every time.
When first physically installed no modem will be detected even when a search is carried out under "Add New Hardware", if this occurs do not attempt to force installation of the modem through "Add New Hardware" as although the installation will appear to succeed the modem will not function. If this has already been done and the modem is listed in device manager but is non functional it should be removed.
You will probably find that an "unknown device" or "PCI communications device" has been detected and may be found in device manager. If so go to device manager, select the device, go to "Properties" and under the "Driver" tab elect to change or update driver. If a list of device types is presented select "modem". Select "have disk" for the driver location and browse to the drivers location. This should install the modem enumerator, and may at the same time detect and install the modem, however if the modem is installed at this time it will probably not work until the system is restarted. If only the enumerator is installed restart the system and the modem should be detected and installed automatically.
Addendum: The following is a method posted by Crustyoldbloke and is for use if the above installation method fails. As always when working with the registry, BACK UP.
Firstly, delete/remove your modem driver from the CONTROL PANEL-MODEM setting.
Then backup your registry.
Now go to START, RUN, and type REGEDIT. Double click HKEY_LOCAL_MACHINE, below it you will see a subsection called Enum, double click it to expand it.
Do the same to the one marked PCI, you should now see some keys marked VEN_*******, expand each one and below it you will see another key marked BUS_******.
Expand that key and each one will show you a name and data in the right-hand pane. One or more of those is your modem and the name will be clear.
Now delete the keys marked BUS_******* with your modem name. Reboot, and Win98 will install your modem.