Aptiva 28.8 Mwave modem and Windows 98

My Dad has an IBM Aptiva 2168-A45 PC which was purchased at least 4 years ago. He just upgraded to Windows 98. When trying to connect to the internet, he gets a message saying that Dial Up Networking could not complete the connection, then somethingabout check to make the modem is setup properly, or something. It refers to error code 630. We’ve checked all his modem and dial up settings. He’s also checked them with blackfoot.net, his ISP. Any advice, good news, bad news? He’s tempted to go back to Windows 95. Don’t know how easy that would be. He’s uninstalled and reinstalled the modem and getting nowhere. Is this modem compatible with Windows 98? Does he need to buy a new modem? I’ve checked IBM’s website and am not getting anywhere.