This driver works with the AOpen Rockwell PCI HCF modem - the part number on the card should be something like 91.12019.103, Ver BA, and it should have on the top right hand corner of the chip side "56VPCI-U/R".
This was downloaded on 17 Feb 2001 from the Acer Netxus web site - they call it an AMI-56VPCI modem. I assume AMI is for Acer Modem Internal - ??
Unzip it into a directory, go back to the Device Manager, double-click on "PCI Serial Controller" and click Reinstall driver, then Search for a new driver, then download from a specific location and Browse to the location on the hard drive where you unzipped the files. You will have to descend several levels - the structure is exactly as provided by Acer. Don't descend into the "nt" directory 'cause it won't work.