Ok, now i've installed this module and figured it out at last:

Use the Part() Method just like the Body() Method and the use SendLineEnc (SendLine or print) to print to that Part of the message.

my $snd = Mail::Sender->new({
    smtp => ...,
    from => ...,
});

$snd->OpenMultipart({
          to => ...,
          from => ...,
          subject =>"TEST",
}) or

    die "Error: $Mail::Sender::Error\n";

$snd->Body(0,0,'text/plain');
$snd->SendLineEnc('TEST EMAIL');

$snd->Attach({
           description => "ATTCHMENT",
           ctype => "text/plain",
           disposition => "attachment; filename=\"xyz.txt\"; type
                            +=\"text/plain\"",

}) or
    die die "Error: $Mail::Sender::Error\n";

$snd->Part();
$snd->SendLineEnc('CONTENT OF ATTACHED FILE');

$snd->Close;
[download]

Two more things: Please do not quote "$vars", there's something about it in perlfaq4 (`perldoc -q 'quote.*vars'`), and: I would never use a module that assumes text/html as default Content-Type for emails!

--
http://fruiture.de