As everybody else has said so far, there is a built-in utility for backing up SBS 2003. You should configure it using the SBS management console and not try to configure it directly. There is a whitepaper from Microsoft that details how to backup and restore SBS2003. It is available here:
You'll notice that the restore procedure is not exactly quick. Here's a quick summary:
- Install SBS from media
- Download and install all drivers
- Download and install latest service pack
- Restore all files and system state
- Restore SQL database
If you don't want to deal with all of that, spring for an image based backup option. Most vendors will provide a lower cost SBS license of their software. My current favorite is StorageCraft's ShadowProtect but you can find any other number of options.