Are you using a program that automatically checks for updated components or Web pages.
What have you got in the Startup folder.
Have you run a full anti virus check?
Have you installed Symantec WinFax or HotFax Message Centre
Are you are using a Lexmark printer. The Lexmark printer software sometimes adds Lexstart.exe to the Run registry key to handle print commands that you send to the printer. This can cause Dial-Up Networking to prompt you to dial your ISP.