Have a look at the Microsoft Dynamics CRM 4.0 Performance and Scalability White Papers here:
http://www.microsoft.com/downloads/en/details.aspx?FamilyId=5852B14A-394C-4898-8374-CAF5E6479EB0&displaylang=en
or
Improving Microsoft Dynamics CRM Performance and Securing Data with Microsoft SQL Server 2008
http://www.microsoft.com/downloads/en/details.aspx?FamilyID=B5BB47A4-5ECE-4A2A-A9B5-5435264F627D