You only need to use the 'RewriteEngine On' once, and you can stick that extra bit anywhere underneath it. Something like this;
Code:
RewriteEngine On
RewriteCond %{HTTP_HOST} ^fragtoss.com$
RewriteRule (.*) http://www.fragtoss.com$1 [R=301]
# Some servers require the Rewritebase directive to be
# enabled (remove '#' at the beginning to activate)
# Please note: when enabled, you must include the path
# to your root vB folder (i.e. RewriteBase /forums/)
#RewriteBase /
#RewriteCond %{HTTP_HOST} !^www\.yourdomain\.com
#RewriteRule (.*) http://www.yourdomain.com/forums/$1 [L,R=301]
RewriteRule ^((urllist|sitemap_).*\.(xml|txt)(\.gz)?)$ vbseo_sitemap/vbseo_getsitemap.php?sitemap=$1 [L]
RewriteCond %{REQUEST_URI} !(admincp/|modcp/|cron|vbseo_sitemap)
RewriteRule ^((archive/)?(.*\.php(/.*)?))$ vbseo.php [L,QSA]