First things first, you want to uncomment use strict;

Second, there's no reason to call the perl script through php when you can just call the perl script itself as a cgi script.

Finally, consider using the following:

print "AUTORE=$tag->{ARTIST}&ALBUM=$tag->{ALBUM}&BRANO=$tag->{TITLE}";
[download]

in your code as well, instead of bunches of "foo",$bar,"baz",$bleh";