Hi,
If you mean the backup facility within Admin, then this just backs up your database. When I say "just", it still covers most of the important things.
To back up the rest of the stuff, you need to ftp it down and archive it.
The database info is what changes the most.
Your backup procedure will also be dependent on where you store your images, database or file system.
By the way, I am sure someone is going to come along in a mo and politely tell you to include a signature with your version no in. That helps people help you. Although all versions I have seen, the backup is just for the DB.
Hope this points you in the right direction. If not, let me know.
Pau Dodman
e-business consultant
Lumino Internet
luminointernet.co.uk