Your listings are kept on Auctiva servers. If you would like to keep a backup the best you can probably do is copy and paste your auction descriptions into microsoft word documents or notepad. Then the worst case scenario if something bad happens you would just have to re-enter prices and shipping options, but the description (which is usually the majority of the listing) would at least be saved.
Auctiva keeps several backups of everything in our database though so the occation should never arrise where you need your own backup
Hope that helps!
Auctiva David