How to tell if out-of-memory condition is approaching

[Mark E. Powell]

I have an app that walks directories and stores data in variables.  For extreme trees, available memory can peter out and the app becomes unresponsive.

Firstly, how can I tell that such an out-of-memory condition is approaching?   Secondly, can anyone point me to a white paper, documentation topic, or best practices document that talks generally about how to handle memory issues on Windows? 

Many thanks in advance

Mark