As with Northwind 'Orders',where when the customers name is entered the address is automatically filled. I am trying to produce a similar effect for a purchase order using the suppliers name/address.I seem to be having problems with producing this effect.
All ideas gratefully received.

Check out the Relationships for the database. Notice that the Orders table is linked (joined) to the Customers table via CustomerId. That is how they are able to pick up the Customer info (see the After Update event for CustomerId. In the same way, the Orders table is joined to the OrderDetails table on OrderId. Then OrderDetails to Products on ProductId and finally Products to Suppliers on SupplierId.

Depending on where you start in the chain, you can get the data you require via these Joins.