Well then you should be reading more about Forms Authentication.
http://msdn.microsoft.com/en-us/library/aa480476.aspx
http://msdn.microsoft.com/en-us/library/xdt4thhy.aspx
http://www.devhood.com/Tutorials/tut...tutorial_id=85

These links have enough material to get you started with forms authentication. This is how you should be handling log-in log-out for your application. using sessions is an old classic ASP technique and has its own drawbacks.