You might be better using a Mutex instead of a lock file. The following code has not been tested on Vista (I don't have the courage to try):

use strict;
use warnings;  

use Win32::Mutex;

# This returns a handle to the mutex, and optionally creates it
my $mutex = Win32::Mutex->new(0, 'appln_mutex_name');

# Grab the lock, or block
$mutex->wait; 


#  This is for testing purposes
# Insert some clever Perl stuff here
print "Hit <RETURN> to continue";
<STDIN>;

# release the lock
$mutex->release;
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