For your convenience I've created sample application. At the top there is FormView bound to Customers table from Northwind via LinqDataSource.
Bellow FormView control there is RadGrid that is bound to Orders and shows the records only for those Orders that match the CustomerID from FormView. You can perform Insert on new Order in RadGrid and CustomerID of the new item will be automatically inserted.
I hope this helps.
the Telerik team
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items.