I am not a big board, only about 60,000 posts, but I am using the following for my backups:
http://www.in-my-opinion.org/in-my-opinion-4529.html
It was designed for phpBB but I found it works well for VB, I recently used it to move from 1 host to another with out any issues (you millage may vary).
Currently I have it running the mysql backup once a day and the files once a week. Every night I have a server at my home go out and download what ever new backups there are and when it is complete remove them from the server.
I keep the backups in a protected directory so as not to be grabbed by the search engines, scheduling is done via cron.
Hope it helps.