I have used Nero BackItUp to back up a hard drive to DVD. It will backup to multiple DVDs and will prompt for the next DVD. Having done it I now get to thinking "How do I restore it, if I need to?".
I now use xxcopy from click here and do a complete clone to another hard disk rather than DVD. Once completed, the hard disk is taken out of the computer and stored. If I ever need it all I have to do is install the backup hard disk as the master and boot the computer.
The only things I back up to DVD/CD are my personal files/documents/data etc.
A good program to buy for cloning/backups is Acronis True Image 8. A number of Forum members including myself have got it. It is an excellent program and much easier to use than Ghost. Suggest you do a search on the Net to find the best price....it is preferable to buy it on CD than do a download because it can be used as a start up CD in case of problems.