Backups should include email, internet bookmarks, work files, data files from finance programs like Quicken, digital photos and anything else you can’t afford to loose. You can easily copy all your files to a CD or another computer on your home network. Also, keep all your original Windows and program installation CDs in a safe place.
How often, you ask? Look at it this way: Any file you cannot afford to lose (what will take too long to re-create or is unique and cannot be re-created), should be located on two separate physical media, such as on two hard drives, or a hard drive and a CD. That type of important information should be backed up daily (if any file information has changed).
If you decide that you want to do a complete hard drive backup, consider these: