There are different things you can do to backup SMP and its components. It all depends a bit on what your environment looks like and what exactly it is that you want to back up.
The most important thing to back up is the CMDB. How to do this is described in the article Backing up the Configuration Management Database in the Altiris™ IT Management Suite from Symantec™ Migration Guide version 7.0 to 7.1 SP2.
Another thing to backup are your reports. This is most easily done by using Data Connector to export the reports in a suitable format. Have a look at the article Configuring data transfer in the Symantec™ Management Platform 7.1 SP2 User Guide.
There are also ways to backup the whole NS. If you have a small environment you can run the NS on a virtual server using VMware and then use snapshots as backups. Another way to do a complete backup is to use a program like Backup Exec to backup everything on the Notification Server computer.