I'd break the problem into a couple of pieces.

1. Obviously, read the comments. They may even be useful &grin;.
2. Determine what each Perl program is supposed to be doing. This may require interrogating users (don't forget the thumbscrews to apply pressure).
3. If they are available, talk to the people who wrote them. This may be more difficult; the live ones may be incommunicado. You'll still need the thumbscrews; I hope you've kept them.
4. Get one of the Perl books, large quantities of highlighters, and oceanic quantities of the caffeine source of choice (I prefer Starbucks) and become the human Perl parsing machine for a while. While this is less than fun, you will soon know more about how to write (and not write) Perl than you've ever wanted to know.