Integration is done with BizTalk, but IMHO there should be a native integration, as CS and Dynamics CRM are in the same business pipeline as the CS is just another sales channel ....
http://blogs.msdn.com/rdonovan/archive/2009/01/05/wiring-up-dynamics-crm-commerce-server.aspx
Commerce Server based on Sharepoint
http://blogs.msdn.com/commerce/archive/2008/12/22/december-community-technology-preview-ctp-is-now-available-for-download.aspx