This is more like a case study: extending regular TreeView ActiveX control with FLL library.

Displaying Windows shell folders in TreeView control with Visual FoxPro FLL
http://www.news2news.com/vfp/?example=577

Some of the features:

- a regular TreeView control is used (MSComctlLib.TreeCtrl)
- the folders are depicted using appropriate images provided by the OS (no extra graphics files required)
- FLL monitors changes in folders
- VFP9 form receives folder change notifications via window messages and redraws the tree accordingly
- older VFP versions can poll recent folder changes using the Timer control
- the tree displays compressed (zipped) folders (Vista)
- VFP code contains no API declarations, most of the complexity moved inside the FLL

Download the FLL and sample PRG code. Unpack to a folder and run the PRG file.
http://www.news2news.com/vfp/downloads/TreeViewExtender_FLL.zip