crypt() question

I am trying to get the same output crypt() does one
one machine to another. I have grep'd thru a perl script
on the server for "crypt" and have found out that the password
it generates is done by crypt($INPUT{'pwd'}, aa). I need to add
additional entries in the password file (offline) with something like

print "Please enter string to crypt: ";
my $string = <STDIN>;
chomp $string;
my $p = crypt($string, "aa");

Yet I get a differant value from the same string
on the server. Could someone clue me in on how
this works?

v/r
-Mike