For years when I needed to determine if a service pack was installed on SQL Server 2000 or SQL Server 2005, I would check the build number and ten search the web to find what the build number was for the latest service pack. Today I was going through the same routine, but when I searched Google, I found a SQL query that would more directly reveal the version and release:
1: SELECT
2: SERVERPROPERTY('productversion'),
3: SERVERPROPERTY ('productlevel'),
4: SERVERPROPERTY ('edition')
Here is the Microsoft KB article.
Here is a chart of all SQL Versions, their names and release dates.