You might want to check out the Perl module Win32::ChangeNotify. This will monitor a file or directory for changes and then from there you can instruct it to do whatever you like when it detects a change. I'd suggest this process:

1. Monitor and watch for change in a while loop
2. On change, run perl commands to output CSV
3. Issue a "system" call for the external Windows app you refer to
4. When done return to 1. (that is stay in the loop).
5. Exit loop if errors occur.

Hope that helps.

Dean