Never dial a connection
While tracing the programme triggering this you might try:
Having a look in the internet seetings, select "never dial a connection" or "confirm before dialing". (Or similar - it's been a while since I set up a windows dial up.)
Alternatively configure a dummy dial up, account use just a single digit so you dont accidentally dial. Set this to be the default.
Either of these will require a manual intervention before a connection gets made.
Good luck!
Memetic
P.S. try googling for the search term windows dials at random it brings up a lot of results!