If you are using CGI::Simple and want to set a P3P header so that cookies on IE6 will work correctly, but you don't want to use a policyref file (you don't need to) you can make this quick fix. Change line 696 from:
push(@header, qq(P3P: policyref="/w3c/p3p.xml", CP="$p3p"));
push(@header, qq(P3P: $p3p));
Now you can correctly set a P3P header, eg:
$cgi->header( -P3P => 'CP="NOI DSP COR NID TAIa OUR NOR"' );
I've got no idea what that compact policy means, but it does the trick. The whole concept behind P3P makes no sense to me.