Many things have changed with SQL 2005, correspondingly we have to change the way we think about troubleshooting performance problems.  The most significant change is the advent of the new Dynamic Management Views (DMV), these are going to take some getting used to and this article helps significantly.  There’s some really good stuff around identifying blocking, something that plagues most of us at sometime or other – well worth a read if you’re responsible for day to day running of a SQL box.

http://www.microsoft.com/technet/prodtechnol/sql/2005/tsprfprb.mspx