As many of you know, only one-to-many and many-to-one relationships can be created in Microsoft CRM 3. To create many-to-many relationships, the most commonly used technique is a “middle” entity, or mapping entity. However, there are several other options for the more pragmatic customizer. Please refer to the CRM-Team blog post:

Gustaf Westerlund
CRM and SharePoint Consultant

Humandata AB