Commerce Server 2007 Capacity Planning Tool

Check this wizard which will help you decide on your Commerce Server 2007 production environment configuration.
http://www.microsoft.com/commerceserver/techinfo/planning/capacity.mspx
You may also have a look at the following pages:
http://msdn.microsoft.com/en-us/library/ms915607.aspx
http://www.diraction.ch/shopdocs/files/Commerce%20Server%202007%20Product%20Overview.pdf