post your stdhead mate. that code what joos showed you is what you need to add. you need to add
Code:
if(isset($CURUSER)) {
above the block code you wan to hide from guest/login
and
goes below the block code so your wrap it around. only current users will see (registered)
so your categories will be from
Code:
categories_block("Cats");
to
Code:
if(isset($CURUSER)) {
categories_block("Cats");
}