SQL Server 2005 database diagram support objects error

Sql 2005 Database diagram support objects cannot be installed because this database does not have a valid owner...

Solution:
1. Right Click on your database, choose properties
2. Goto the Options Page
3. In the Dropdown at right labeled "Compatibility Level" choose "SQL Server 2005(90)"
4. Goto the Files Page
5. Enter "sa" in the owner textbox.
6. Hit OK

Reference: http://geekswithblogs.net/shahed/archive/2007/11/19/116940.aspx