When I came home from work tonight, there waiting on my was my copy of Professional Microsoft SQL Server 2008 Administration from Wrox (link goes to Amazon). I'm not listed as one of the primary authors (so I didn't get my face on the cover), but I did update and add to chapter 9, Securing the Database Engine. It was great working with SQL Server 2008 and getting to write about the new security features found in it. One of the other things I tried to do was bring some of my systems/security architecture experience and look at the server upon which SQL Server is installed. So you'll find coverage about what groups to be concerned about as well as what rights (found in the local security policy) that you'll need to be aware of and why they're important. I also spend time talking about the SQL Server related groups and the normal permissions on the SQL Server folders and where you have to think about adding to that (such as protecting your backups).
If you're looking for the book on how to administer SQL Server 2008, here's the book you want. There are some great authors (Brian Knight, Ketan Patel, Wayne Snyder, Ross LoForte, Steven Wort, and Geoff Hiten) who contributed some great material. I am rather humbled to get a chance to write a chapter alongside their work.