How can I create new login in SSMS 2008?
Open the Window again to create a new login.  Use the "Search" button to find the Windows login you wish to create an account for.  Then you can click the "Script To" button at the top and get the actual T/SQL Script.  It should look something like

CREATE LOGIN [KAWMIN-PC\Classic .NET AppPool] FROM WINDOWS


The UI doesn't always work correct for creating logins with spaces or other reserved characters.

Once you have the T/SQL script correct any issues and run the script and the login should be created.  If there is an error post the error message to the site.