Best backup plan for a Win 03 Server

I have a Win 2003 server in a simple configuration. It has a C drive for the OS and a E drive with all the company’s data. I also created an ASR backup on a floppy and a tape using NTbackup.

When setting backups, is it best to backup EVERYTHING (C and E) or is backing up only the E drive and the system state good enough to recover from a total meltdown??

Thanks for the advice