Alright, so I poked around and figured my best bet was to run my own query. So I did this:

$categories_description_query = "SELECT categories_description
FROM categories_description
WHERE categories_id = :categoriesID";

$categories_description_query = $db->bindVars($categories_description_query,
':categoriesID', $categories->fields['categories_id'], 'integer');
$categories_description = $db->Execute($categories_description_query);

Then later I can call $categories_description->fields['categories_description']

Hope this helps anyone else stuck with the same problem.

Cheers,
cw