Since you've not mention what OS you're running I've assumed a recent version of Windows (2000 onward).
Nero CD/DVD writing software has a command-line application NeroCmd (search on Google for more details). That should enable you to schedule Nero though a batch file with Task Scheduler (or your At/Cron daemon of choice) to back up to a rewritable disk every night assuming you wanted unattended 24x7x52 operation.
Something to be careful of is monitoring the backup regularly to ensure it's successful - could be expensive if someone pops out the DVDRW and forgets to put it back in.
I'm sure you could probably do this with other writer software too...