Items should be the 'many' side to orders. You have the keys backwards. You need the OrderID in your lineitems table and not the Items ID in the orders.
You also need a Products table (which holds the Make, Model, Price) which is used for selecting your Products to insert into the Items table. I see no Quantity field in Item either.
To allow creation of records in a portal, you need to turn it on in your relationship dialog. So double-click the = between Orders and Items. At the bottom, enable 'allow creation of related' on Items side only. :^)
Thanks worked perfect!! i Guess i should have noticed that :S