The following information was found in the Microsoft Knowledge Base when a user could not get his dialup scriptor to work after re-installing the Dial-Up Network. Thanks to Mike Whiting for finding this little gem:

Problem:
Dial-Up scripting may no longer work after Dial-Up Networking is Reinstalled.
Even though all the components are there and appear to be Ok, they are not.

Cause:
Reinstalling Dial-Up Networking overrides entries in the Registry that Dial-up Scripting requires to intercept the normal Login Procedures.

Resolution:
Use Control Panel Add/Remove Programs, to reinstall scripting tools by using "Have Disk" button under Windows Setup Tab, select Rnaplus.inf.
CD ROM Path= x:\Admin\Apptools\Dscript
Click the "Slip and Scripting for Dial-Up Networking"
Your old scripts should still be in place.