With the stsadm backup operation, you can do full or differential backups, not incremental. You select between full and differential using the
If you use the
-url parameter to the backup operation, the backups are done at a site collection level. If you use the
-item parameter, you can backup at the content database or web application level.
You'll probably need to do some playing around with the
-showtree parameter to understand the syntax required for the
-showtree will give you a tree of everything in your server farm, and mark what is going to be backed up if you were to remove the
See this TechNet article, especially the "Correction" community content by Mark Vogt at the bottom of the page for details about how to get this setup.