Backing up an SBS 2008 system is a vital part of the daily routine. SBS 2008 can reliably automate this for you, without the need for additional software, once the configuration is complete. I would recommend using at least two and ideally, three USB disk drives that can be plugged into the server for the backup, but easily swapped on a regular basis to enable you to take the backup off-site.
These drives would be used only for the SBS backup and are specially configured in SBS. Provided that one of the configured set of drives is attached to SBS 2008, it will continue to take backups.
For security, I would advise that the drives are swapped daily or weekly. Also that the non-active drives are removed from your premises while not connected to the server and stored in a secure, ideally fireproof, location. However, as these systems contain hard disks, they should be handled with care and just like tapes, they are still prone to wear. You should...