Try running the following in a command window
C:\> control modem.cpl
If the above did not work check and see if the "PnP ISA Enabler" service is running. I think it is listed as Plug and Play in the services list.
If it is stopped or disabled try starting it and running the command above again.
Failing that you have some files missing. Reapply the Service Pack. !!!Make a backup First!!!
Remember it is Microsoft you are dealing with!!