New Files Problem

I have shared a folder on my main PC (Vista Home Premium SP1). All the files
that folder, when I first shared it, can be viewed and accessed by other
computers in my network (laptop with Vista Business SP1, PC with Vista
Ultimate SP1, and of course my iMac with OS X). The problem is that none of
the networked computers can see any new files that are added to the folder.
I have to stop sharing the folder and then share it again for the new files
to be viewed and accessed. Of course any additional files I add later cannot
be viewed and I have to repeat this procedure again. Any idea what's going
on?