Well the problem you will have now is indexed content from your original vB installation and now your XenForo installation so you will need two lots of redirects, assuming you don't want any dead links.
One for vB to the new XenForo URLs and one for the old XenForo URLs to the new XenForo URLs.
Both should be simple enough to set up.
This for example is the redirect I have in .htaccess after moving my installation from /community to the root.
Code:
RewriteRule ^community$ / [R=301,L]