The answer to John's question comes in two parts. Firstly you need software which can be scheduled to run in the back ground and at preselected times back up your chosen files to a suitable destination. This might be CDs, ZIP discs, a flash drive, a virtual drive on the web, another disc drive in your computer, a drive on another machine on your network or an external disc drive which is easily disconnected and taken away if required.
One of the easiest programs to use and one which I have found to be very reliable can be downloaded for free from http://www.karenware.com/powertools/powertools.asp
It will allow you to select which files you wish to copy, where you wish to copy them and when. The only slightly technical thing you need to do is to copy the programs icon into the startup folder so that it will happily run in the background.
Once you have set up your schedule it will backup everything you have selected and then update your files on a regular basis. It will only copy files which are newer than the originals once the first backup has been made. You can even set it to delete files and folders on the destination drive to reflect any deletions you make on the source drive (although I really wouldn't advise this - for obvious reasons).
I've indicated the range of devices you can use for storing the backups but the one I use is a Media Centre from Western Digital (for less than £200). These have a range of hard disc drive sizes between 160GB and 256GB and is connected to your computer via either USB (preferably 2.0) or FireWire. (It is also able to read a wide range of memory cards from cameras, etc.)
If you have an older computer with only USB 1.1 you can still use the device quiet effectively - it will just be a bit slower. However it is quite easy to add USB 2.0 ports to your PC - these come in the form of a PCI card. They often give you as many as four extra USB ports at the rear of the computer and you can then add a header which fits into a spare floppy disc drive bay or a spare CD Drive bay and this gives you another four sockets at the front of the computer. All eight sockets are powered. It is also possible to add externel hubs to these ports so you can place these on your table top in installations where the computer is a little hard to get at. (Some modern monitors often have additional USB sockets built into them for added convenience.)