As per Steve's reference they are helpful to obtain status of SQL instance and if you want to know more about DMVs then refer to SQL 2005 Books ONline, also refer to http://sqlserver-qa.net/blogs/perftune/archive/2007/08/05/1262.aspx for your information.
-Satya SK Jayanty
SQL Server MVP (Follow me @sqlmaster)
Author of SQL Server 2008 R2 Administration CookBook
SQL Server Knowledge Sharing network