Thanks very much for you replies, I guess it answers my questions, the photo's are the precious things, all my documents etc are backed up on other computers, so I guess an external drive is the way forward, with cd/dvd backup also.
As regards to the "backing up the operating system," the reason I asked was because my daughters laptop just doesn't work-and it looks like I need to re-install Windows XP
http://www.pprune.org/forums/showthread.php?t=308361 but unfortunately the software was pre-loaded. (So I don't have a disc).
Guess I want something to put into my laptop should the same thing happen.