if you are running SQL Server 2008 on Windows Server 2008 R2 (specifically this OS only) then you should absolutely ensure that you’ve installed the following fix:
976700 An application stops responding, or experiences low performance, or experiences high privileged CPU usage when many large I/O operations are performed in Windows 7 or Windows Server 2008 R2
http://support.microsoft.com/default.aspx?scid=kb;EN-US;976700
In this scenario, the key symptom is high kernel times, – see the perfmon counter: Process(sqlservr)\% Privileged Time
