With the modem in the system, boot windows up - if windows detects the card on start up, then follow the onscreen instructions in Add New Hardware Wizard.
If it has previously detected it but not installed it, then go to device manager & look for an entry called either 'pci communications device' or 'unknown device'. It should have a yellow exclaimation mark next to it. Double click on the entry to open its properties, then select to reinstall or update driver.
If neither of the above are applicable (ie win98 hasn't detected it & no listing in device manager) then goto control panel - modems & add new modem. Click the box labelled 'Don't detect modem. Select from list'
In all of these cases, when the wizard starts up & click on the 'have disk' button & direct windows to the location of your driver.
If you receive a message telling you that the driver wasn't written specifically for that device, ignore it & continue. It may that the driver is the wrong one, but often I find with conexant modems, you receive this message regardless so don't just assume the driver is wrong.
Once installed, go back to C/P & Modems. Click on the diagnostics tab, highlight the modem thats listed & click on the 'more info' button. If the modem is installed correctly, after a few seconds you will see a list of AT commands appear. Otherwise, you will get an error message.
Let me know how it goes.