Just bumped into Stunnware's (Michael Hohne) web site and saw he released his initial version of the Filtered Look up for Microsoft Dynamics CRM 4.0. It comes complete with documentation. This tool was initially a workaround to filter lookup results, but it grew to a tool set with a lot more functions.
The Filtered Lookup Dialog for Microsoft Dynamics CRM 4.0 contains the following new features:
Besides the new features, it still includes the features that have been present in the Custom Lookup Dialog for Microsoft Dynamics CRM 3.0.