I found a way to collapse all the forums on the main page of a forum by changing the following in index.php:

$viewcat = ( !empty($HTTP_GET_VARS[POST_CAT_URL]) ) ? $HTTP_GET_VARS[POST_CAT_URL] : -1;

changed to

$viewcat = ( !empty($HTTP_GET_VARS[POST_CAT_URL]) ) ? $HTTP_GET_VARS[POST_CAT_URL] : 1;

What that gives me is ALL the forums hidden/collapsed until I click on a category, and then it expands to show the forums in that category.

What I want instead is to be able to pick and choose which categories I wish to collapse, rather than a global command.

Any wisdom to share?