modem problems after MS upgrade

I downloaded and installed Microsoft upgrade KB842773.
Upon restart, I began having modem problems when
connecting to the Internet. The process would hang up
during the logon (on Earthlink, it happened during
the "projection phase"), seriously enough that the PC was
basically crashed. Couldn't even get Task Manager to
work. I am running an HP pavilion 7970, 1.5 ghz Pentium
4, 128 mb rdram, with a Lucent Win 56K modem.
Earthlink's so-called support says, talk to HP or
Microsoft. I do blame the upgrade, because I did a
system restore to the day before the upgrade, and am now
able to use the modem again. Anybody have any ideas?
Thank you, Pete