[...]for ($i=0;$i<=$SIZE;$i++) {
   $_=$LINES[$i];
   if (/<!--begin-->/) { 

      if ($entry_order eq '1') {
         print GUEST "<!--begin-->\n";
      }
      
      ## Das hier habe ich eingefügt ##
      $FORM{comments} = break_lines($FORM{comments});
   
      if ($line_breaks == 1) {
         $FORM{'comments'} =~ s/\cM\n/<br>\n/g;
      }

      print[...]

sub break_lines{
  my $text = shift;
  my $maxlength = 80;
  my @commentlines = split(/\r?\n/,$text);
  for my $line(@commentlines){
    if(length($line) > $maxlength){
      my $index = rindex($line,' ',$maxlength);
      if($index != -1){
        $line = substr($line,0,$index)."\n".substr($line,$index+1);
      }
      else{
        $line = substr($line,0,$maxlength)."\n".substr($line,$maxlength+1);
      }
    }
  }
  $text = join("\n",@commentlines);
}