My teammate Lyudmila is maintaining her own TechNet blog where she writes articles related to SQL Server security. You can access her blog at http://blogs.technet.com/lyudmila_fokina. Her blog is written in Russian, but the samples she includes should be easy to follow, and you can use an online translation tool for the rest of the text.
Her latest article is a very interesting suggestion on how to use SQL Server Agent jobs to provide a scheduled temporary elevation of privileges. You can find the whole article at http://blogs.technet.com/lyudmila_fokina/archive/2009/06/11/sql-server-agent-jobs.aspx.
-Raul Garcia SDE/T SQL Server Engine