I didn't test it, but I'm almost certain this should work.
find:
$news_forum_id = 5;
add after:
$news_forum_id2 =6;
find this line:
$result = $db->query('select id, subject, num_replies, posted from '.$db->prefix.'topics WHERE forum_id='.$news_forum_id.' ORDER BY -posted LIMIT '.$limit.';')or error('Unable to fetch topic list', __FILE__, __LINE__, $db->error());
Replace with:
$result = $db->query('select id, subject, num_replies, posted from '.$db->prefix.'topics WHERE forum_id='.$news_forum_id.' OR forum_id='.$news_forum_id2.' ORDER BY -posted LIMIT '.$limit.';')or error('Unable to fetch topic list', __FILE__, __LINE__, $db->error());
All this will load news from 2 forums. If you need more, just make similar changes in the WHERE clause. For example if you want to limit to 4 forums do something along the lines of:
WHERE forum_id='.$news_forum_id.' OR forum_id='.$news_forum_id2.' OR forum_id='.$news_forum_id3.' OR forum_id='.$news_forum_id4.'
for the WHERE clause. Also define the variables for each of the $news_forum_id*
-------------------
Alternately if you want to load from all forums, just don't specify the WHERE clause which currently limits the SQL query to specific forum_ids.
Query for getting all forums:
$result = $db->query('select id, subject, num_replies, posted from '.$db->prefix.'topics ORDER BY -posted LIMIT '.$limit.';')or error('Unable to fetch topic list', __FILE__, __LINE__, $db->error());
Hope this helps