LINQ, WHERE clause issue

Question: Why lines 5 and 6 giving me trouble?

How can I fix this. I have used this sort of syntax for years in SQL work. What is the equivalent in LINQ (vb.net)?

            Dim ODs = (From od In db.tblOrderDetails Join o In _
                               db.tblOrders On od.OrderID Equals o.OrderID Join c In _
                               db.tblCustomers On o.CustomerID Equals c.CustomerID Join s In _
                               db.tblSoftwares On od.SoftwareID Equals s.SoftwareID _
                               Where o.OrderID = IIf(intOrderID = 0, o.OrderID, intOrderID) And _
                                o.CustomerID = IIf(intCustID = 0, o.CustomerID, intCustID) _
                               Order By c.FirstName & " " & c.LastName _
                               Select CustName = c.FirstName & " " & c.LastName, _
                                      od.OrderID, o.OrderDate, s.Title, od.Quantity, s.UnitPrice, Sub_Total = od.Quantity * s.UnitPrice).ToArray()

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Please see: http://developwith.net/2012/07/20/where-if-and-where-iif-linq/ if it could help. I may need some help in its implementation.