from the command line:

perl -pe '$skip=0 if /^end$/; next if $skip; $skip=1 if /^begin$/' dat
+a.txt
[download]

Or a little more drawn out:

#!/usr/bin/perl

use warnings;
use strict;

my $skip=0;
while(<DATA>)
{
    $skip=0 if /^end$;
    print unless $skip;
    $skip=1 if /^begin$/;
}

__DATA__
a
begin
1          <-----  delete
a          <-----  delete
2          <-----  delete
end
c
begin
c
end
a
begin
1
[download]