The latest generic driver for the winmodem from Lucent/Agere is version 8.30 and it changes the name of the modem to Agere Winmodem.
http://www.agere.com/entnet/modem_driver2.html
This driver self installs and can not be installed using the Hardware Wizard. Cancel the HArdware Wizard when it comes up and run the modem830.exe driver.
The modem should be uninstalled by running the LTREMOVE.EXE program that is installed to your hard drive when the driver is installed.
Try running the LTREMOVE program and then shutting down and removing the modem.
Boot back into windows allowing the BIOS and windows to see the modem is gone.
You may have to try several PCI slots. I have seen some systems very stubborn about these modems.
I would leave the serial com ports in the BIOS enabled as disabling them sometimes confuses Windows about numbering them.
The modem should install to com port 3 by default but if its installing to higher numbered ports with each failed driver install Windows is marking the ports in-use and the next install places the modem on the next higher port number.
Once this starts happening it can be hard to recover, but you might be able to reclaim the in-use com ports.
http://www.modemsite.com/56k/xptip.asp
Personaly I think this is a driver problem as the Agere software modem "had" the same problem and the newest driver for it seems to have fixed the problem.