Filter data in a CRM lookup field

Curt Spanburgh posted this message on the Sandbox: Custom Lookup Dialog for Microsoft Dynamics CRM 3.In this post he describes that it is possible to filter the data in a lookup box. He also gives an example which uses data on the form to filter the lookup data. For testing purposes I have used the code below. It should be placed in the form onload of the account entity. It does filter the lookup