With a small change in the podvars.pm You can have different header.html
files for different categories.
This can be used to blockout the Adult categories, or to put ads or
comments in any of the categories.

How to do it:
if ($pod_dir =~ "Asimov")
{
open (READIT, "$pod_templatedir/asimov.html");
}
else
{
open (READIT, "$pod_templatedir/header.html");
}