I don't have the Northwind database but I'm guessing you want something like this for your FROM clause.
from orders o
inner join orderDetails od
on od.orderid = o.orderid
inner join products p
on p.productid = od.productid
inner join suppliers s
on s.supplierid = p.supplierid
inner join Employees e
on e.EmployeeID = o.EmployeeID
Be One with the Optimizer
TG