There is also the module Date::Parse that can help. I don't know its relation to Time::ParseDate but I have used it to parse email dates fairly handily.
Usage is as follows:
use Date::Parse qw(str2time);
my $unix_time = str2time("Tue Sep 25 15:25:43 2001");
print "$unix_time\n";
$unix_time = str2time("04/18/00 11:10 AM");
print "$unix_time\n";