Check Login details before post - Classic ASP

I have usernames and passwords stored in a MS SQL Server, The passwords have been encrypted When someone Logs in I want to check the user name and password is correct when they click the login button. If the details are correct then allow then to proceed to the next page. if it is a new user then add them to the database, But If the password is Incorrect then a message should appear saying invalid password and form should not and load the next page If the user name and login details are correct then I would require a 2 session variables to be created