Hi iojam and thanks for your reply, I was hoping to generate the sitemap from the index page generated by vBadvanced rather than the forum page.
At risk of sounding like a right n00b, why can't the sitemap be generated from the index page, is it really so difficult to adjust the settings?
I've noticed that I can add the string into the robots.txt file to inform search engines where the sitemap is but that doesn't help me with Google Webmaster which is currently looking for the sitemap in the index page - I appreciate what you are saying about adding the
http://www.xxxxxx.com/forum in webmaster account and submit
http://www.xxxxxx.com/forum/sitemap_index.xml.gz as a sitemap.
Incidentally, is there any benefit to generating the sitemap from the forum page rather the index page created by vBadvanced???