It is likely that your 98se cd does not have a native driver for your lt winmodem. If you manually select a driver, windows will not give you an error message if the selection is incorrect.

In the absence of information as to the modem manufacturer and model (so as to obtain the specific driver) I would install the Agere driver. As far as I know, it should not ask you to select a com port - these modems were designed to configure a "virtual" port