Creating A Logon System To Check Users In SQL2008 Express?

I am currently creating an application to track timekeeping (a clock in/out system) and I am trying to work out the best way to do this.

I have a Main Form which contains buttons to ;

- Log in
- Out for Break
- In from Break
- Log out

When a user presses the "log in" button the logon form appears, the user then enters their username and password. What happens next is where I would like the help.

Process is as follows:Click Logon Enter Username/Password Check Logon Form for errors (eg no password etc) Check User is in Database (using SQL query) If user is in DB and username and pass are ok then refer back to the main form to perform Stored Procedure for what the user wants to do (eg logon or or out for break etc). Set label on main form to show user as logged on My question is should I be using a public variable and calling the main form again or in the user logon form having 4 options and using an IF ELSE to select the appropriate Stored Procedure?