Ok, I just downloaded jdownloads to see how the database is structured. Try this:

if ($option == 'com_jdownloads') {
  $catid = JRequest::getInt("catid", 0);
  $download_id = JRequest::getInt("cid",0);

  if ($catid == 0 and $download_id > 0) {
    $query = "select cat_id from #_".
    $query .= "_jdownloads_files where file_id = " . $download_id;
    $db->setQuery($query);
    $catid =$db->loadResult();
  }
  if ($catid == 1) return XXX;
  if ($catid == 2) return YYY;
  // etc.
  // Replace XXX, YYY etc with the module ids to return for each category.
}

answer to 1st question:

if ($option == 'com_jdownloads') {
  $catid = JRequest::getInt("catid", 0);
  $download_id = JRequest::getInt("cid",0);

  if ($catid == 0 and $download_id > 0) {
    $query = "select cat_id from #_".
    $query .= "_jdownloads_files where file_id = " . $download_id;
    $db->setQuery($query);
    $catid =$db->loadResult();
  }
  if ($catid != 1 and $catid != 2) return XXX;
  // Replace XXX with the module ids to NOT show if the item is in category 1 or 2.
}


Answer #2:

I'm not sure what you mean by integrating them. Are you saying you want to just echo some HTML instead of including the modules? Or as well as including the modules?

ok, so instead of the return statement, you can put in a series of echo statements, best put inside {}.

e.g. instead of this:

return XXX;

put this:

{
  echo "<h3>Title here</h3>";
  echo "<p>content here</p>";
  // etc etc.
}

Thats's what i like to do. I'm only stuck at including the JDownloads script too. That's how i did it but it doesn't want to work.

if ( $option != "com_search"

and ! ( $option == "com_weblinks" and JRequest::getVar("id") == "13" )

and ($option == 'com_jdownloads') {

  $catid = JRequest::getInt("catid", 0);

  $download_id = JRequest::getInt("cid",0);

  if ($catid == 0 and $download_id > 0) {

    $query = "select cat_id from #_".

    $query .= "_jdownloads_files where file_id = " . $download_id;

    $db->setQuery($query);

    $catid =$db->loadResult();

  }

  if ($catid != 4 and $catid != 17)

}){

echo "test";

}

Thanks this works now great.
The only thing i try to do now is to make another module with the same script above, but this time the script should redirect people to the registration page (index.php?option=com_comprofiler&task=registers).
I tried some methods but somehow i do it always wrong.