If you want to roll your own it is easily achieved using % and <>. Piping to more/less is more or less traditional ;-) I recommend you use one of the modules if you want robust and portable, although a straight pipe to more will work on *nix and Win32.

my $lines = 2;
while(<DATA>) {
    chomp;
    print;
    $. % $lines == 0 ? <> : print "\n";
}
__DATA__
foo
bar
baz
boo
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