I think what is happening is that the

<>;
[download]

is reading one line from the file that you dragged onto it, then Perl is exiting.

Try

print "TEST\n";
print "ARGV: ..@ARGV..\n";
<STDIN>;
[download]

On my Windows XP, drag and drop is not working at all for perl files. Did you have to set some extra registry/ftype/assoc setting? Double clicking runs okay for me.

Updated: Oh, yeah, the whole pl2bat step. Yeah, that works.