While I haven't specifically tried backing up across the network, I use Microlite BackupEdge on all commercial Unix and Linux installations with superb success and excellent disaster recovery tools. It also has how-to's for backing up other PC's over the network. You can download a free, full-version, 60-day evaluation at
www.microlite.com. Be sure to download the appropriate version for your version of Linux. Cost of the full package is around $200-300, dirt cheap for the performance it does.
BackupEdge also does backups to all types of DVD burners! ON customers with small servers, less than 4.7GB per backup, it beats *any* tape system by a mile!