By default vBulletin only displays the forum on the home page by display order. If you want it to sort by the forum title then you need to change the code a little, and I mean just a little.
Open file includes/adminfunctions.php and change the word displayorder to title int he Order BY sql statement.
find the line:
// get the vbulletin->iforumcache so we can traverse the forums in order within cache_forum_permissions
$newforumcache = $vbulletin->db->query_read("
SELECT forum.*" . ((VB_AREA != 'Upgrade' AND VB_AREA != 'Install') ? ", NOT ISNULL(podcast.forumid) AS podcast" : "") . "
FROM " . TABLE_PREFIX . "forum AS forum
" . ((VB_AREA != 'Upgrade' AND VB_AREA != 'Install') ? "LEFT JOIN " . TABLE_PREFIX . "podcast AS podcast ON (forum.forumid = podcast.forumid AND podcast.enabled = 1)" : "") . "
ORDER BY displayorder
Change the displayorder to title.
Now go into the vBulletin admin page > forum manager and hit on button Save Display Order to refresh the cache.