Get it here: http://www.microsoft.com/downloads/details.aspx?FamilyID=E9C68E1B-1E0E-4299-B498-6AB3CA72A6D7&displaylang=en .
Service Pack 3 for SQL Server 2005 has been recently released. You can get it here . Note that now there are different versions depending on what SQL Server you are using (Express, Express with Advanced Services, etc). The Books Online has also been updated...