What would you want to backup and how? Is it everything or just the Windows partition, for example? And are you putting that on a different storage medium or the same (e.g., on an external HDD or on the same internal one)? Are you after a local solution or would you want to entrust the power of the interwebz to look after your files?
If you haven't really thought of these, I'd suggest getting an external hard drive (of equal or greater capacity than your own) and just copying everything across. I'll go look for a Windows application that makes it easier but it's really simple idea - you keep a copy of all your data and you need to do that every once in a while - probably weekly is a good suggestion but it depends on how often do you change stuff.
EDIT:
After looking around, I think I've found two solutions that shoud serve your purpose.
1. It's called "robocopy" and you already have it. It's included as part of Windows, although it's a command line tool. There is a GUI for it though [http://www.softpedia.com/get/System/OS-Enhancements/RoboCopy-GUI.shtml]. If it were me, it's probably what I'd go for.
2. Just the Windows Backup and Restore feature. After looking at several third party tools, it hit me that Windows probably has something already - I opened the Start meny and found Backup and Restore. It seemed pretty straight forward to set up and it's probably what I'd recommend for you.
