There are several methods of backing up your system. The most common way is to use a tape drive with a capacity to retain all of your programs and data. It should also be capable of backing up all your system files as well as the registry and reliably restore them when you need them. The one most important step is to have a current "Startup Disk" without this disk, you could be facing loosing your operating system and unable to restart the computer. Most new computers have the capability to boot from the CD ROM drive so if you have your original equipment manufacture's install or restore disk you can restart and rebuild. However in some case beware, this option of restart can result in total data loss. As a worse case scenario, If you have the operating disk, the reg number to go with it and a bootable floppy disk, you can still restore your system back to what is was the day you bought it. This illustrates the need to make sure you have your system disks and appropriate licensing at all times. Do not lend your disks to others, it may and most likely is illegal (read your license agreement) and it puts you into a position where you don't have your disks when you need them.
As a rule of thumb, providing you have your system disks and a known good backup of your system on tape or CD you should have no problem successfully restoring your system to a state just prior it's failure. Which leads us to the question..How often should I backup? Backup as often as you need to. that is. if you spend 3 hours a week entering data, is it worth backing up your entire system each day? Most likely not, however you may want to consider backing up only the files you use for the day and skip the operating system and all the applications files, who knows they may even fit on a floppy disk. It is still important to have a current Startup Disk on hand at all times. Any time you install a program, you should make sure you update the startup disk. Also anytime you install a rather large program or update your operating system, consider backing up your registry files so if the installation fails you can restore it back previous the install. For more information on backing up your system... Contact your computer service provider.