It looks like there is a mistaken assumption on the ability to reference the external query during a subquery. You can, using aliasing...
Select *, (Select Sum(OrderTotal) From Orders Where SalesmanID=S.SalesmanID)
From Salesmen S
This is a crude example (just the only one that comes to mind that is not specific to a business situation), when you would probably be better off using a direct join, but there are cases where you would not. It uses the aliased table information in the criteria.
Edit: Whoops, looks like I jumped the gun, this is covered in the 3rd article in the series..