Does a table relationship diagram exist for Dynamics NAV

Hi,

I'm new to Dynamics NAV, Navision (with the exception of a DOS based version!) and I'm also new to this forum. I'm very familar with SQL Server 2000 and 2005 and I have been tasked with creating some Business Intelligence components in SQL Server 2005 with Dynamics NAV5 as a data source. Is there a data dictionary available please. I'm particularly struggling to find a diagram which shows how the core tables relate to each other. There must be an easier way to do this as opposed to reverse engineering the table relationships from the table descriptions.

Any help would be greatly appreciated.

Thanks,

Kieran.