you're looking for the Win32::ChangeNotify module. from the doc:

NAME 
Win32::ChangeNotify - Monitor events related to files and directories



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SYNOPSIS 
	require Win32::ChangeNotify;


	$notify = Win32::ChangeNotify->new($Path,$WatchSubTree,$Events);
	$notify->wait or warn "Something failed: $!\n";
	# There has been a change.




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DESCRIPTION 
This module allows the user to use a Win32 change notification event object from 
Perl. This allows the Perl program to monitor events relating to files and 
directory trees. 

The wait method and wait_all & wait_any functions are inherited from the 
"Win32::IPC" module. 

~Particle *accelerates*