By just checking the file sizes, this will work a lot of the time to differentiate the two files:

#!/perl/bin/perl -w
use strict;

my $file1     = "2006.txt";
my $file2     = "2007.txt";
my $file1size = -s $file1;
my $file2size = -s $file2;

print "The files have ", $file1size == $file2size ? "the same" : "diff
+erent", 
  " size.\n\n";
[download]

In what way did diff not work? Diff should be able to do exactly what you're trying to do...