Do you get extra credit for using CPAN? ;)

Date::Manip is able to parse a wide variety of date formats automatically. There's half the assignment, already done.

I can't remember if Date::Manip is a core module or not. If not, you can download it from CPAN, or if you're an ActiveState user, just pull it in with PPM.

From the Date Manip POD:

In the documentation below, US formats are used, but in most (if not all) cases, a non-English equivalent will work equally well.

1. Parsing a date from any convenient format

  $date = ParseDate("today");
  $date = ParseDate("1st thursday in June 1992");
  $date = ParseDate("05/10/93");
  $date = ParseDate("12:30 Dec 12th 1880");
  $date = ParseDate("8:00pm december tenth");
  if (! $date) {
    # Error in the date
  }
[download]

Even if you're not allowed to use the Date::Manip module, at least look at its source code so you can see how it does all those neat tricks!