Check if file is overwritten

[Esben Skov Pedersen]

How do i check if a file is overwritten by another program, while my script 
is running?

I have to monitor changes and act on them on the fly. 

It only has to work on windows, so perhaps it is possible to set op a hook 
to the system. I saw that done on a folder at one time, but i can't find 
the example now. 

I would rather that it uses a minimum of CPU, since the program always will 
be running. Does anybody know the solution?

/Esben