How to determine which version of SQL Server 2005 is running

To determine which version of Microsoft SQL Server 2005 is running, connect to SQL Server 2005 by using SQL Server Management Studio, and then run the following Transact-SQL statement.

SELECT  SERVERPROPERTY('productversion'),
       SERVERPROPERTY ('productlevel'),
       SERVERPROPERTY ('edition')

Source :: http://support.microsoft.com/kb/321185