"Driver={SQL Server Native Client 10.0};Server=myServerAddress;Database=myDataBase;Uid=myUsername;Pwd=myPassword;"
Note: The second method, with the driver, has shown some compatibility problems with some databases.
In the above two examples, substitute the variables where:
myDataBase and myUsername and myPassword are what you've already specified in the control panel under MSSQL databases. myServerAddress can be 'localhost' or you may need to specify '.\SQLEXPRESS'
Lastly, if you are not sure how to use that in context of the code, you may use this sample code: