At least one of the three ($user, $pass and the DSN itself) seems to be wrong or not to ADOs liking. I assume that you set both your $user and $pass to a non-empty value, and that they do both print out to what you expect if you print them?

I'm no expert with ODBC connection strings - to check that the correct drivers are available, have you tried configuring a named ODBC data source and connecting to that through DBD::ODBC?