Troubleshooting Performance Problems in SQL Server 2005
http://www.microsoft.com/technet/prodtechnol/sql/2005/tsprfprb.mspx
10 Baselining Tips for SQL Server: Lessons From the Field
http://www.sqlserver-performance.com/gv_baselining_tips.asp
Monitoring and Tuning for Performance
http://msdn2.microsoft.com/en-us/library/ms189081.aspx
Establishing a Performance Baseline
http://technet2.microsoft.com/WindowsServer/en/library/1033.mspx?mfr=true