Thanks Ed, I'm going to be writing this in VB as an ActiveX control (probably write the main system in VB too!

I found a solution in MSDN but it relates to VS.NET - even though it's not available yet!

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>>There's a family of API calls that can be used to monitor a folder or subtree for changes, triggering an event at the OS level whenever certain classes of changes occur, such as the addition or deletion of a file to a folder. The API functions require a callback, so it can't be implemented just in VFP with the DECLARE...DLL syntax; you'll need an ActiveX control or FLL that will hand you a callback address and will raise a UI event whenever a change is detected. If you like, I can dig out the information for the API calls; you can create the necessary ActiveX containing a callback function using VB.
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>FWIW, the API calls involved are FindFirstChangeNotification(), FindNextChangeNotification(), FIndCLoseChangeNotification() and then one or more of the event monitoring APIs such WaitForSingleObject().
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>There's detailed C code available in the MSDN library docs under the topic "Monitoring Changes in a Directory or Directory Tree" in the Platform SDK: File Storage area. It uses WaitForMultipleObjects() rather than WaitForSingleObject(), and polls continuously, so that no callback is invoked. You could use this as a template for an idle event in VFP.