Uh, what's the problem with Date::Calc's Delta_Days()?

   use Date::Calc qw/ Delta_Days /;

   my $date1 = "01/12/2003";
   my $date2 = "01/01/2004";

   my( $d1, $m1, $y1 ) = split( /\//, $date1 );
   my( $d2, $m2, $y2 ) = split( /\//, $date2 );

   my $dd = Delta_Days( $y1, $m1, $d1, $y2, $m2, $d2 );
   print "diff is $dd days\n";
[download]

(note: I noticed you had dd/mm/yy, but I got lazy ;)