my vbdownloads works perfect on 4.2! I am pretty sure you have to make your own tabs with the Nav Manager on 4.2 the default link would be vbdownloads.php just try www.yoursite.com/forum/vbdownloads.php and see if it works if yes you just need to set a tab in the nav manager
I actually meant that the default vbdownloads.php was default for the downloads product not the navbar but it's very good that you pointed that out as I'm sure it will help others!