A realistic pessimist! Yes, you should back up your hard drive and registry, but I wouldn't worry about the latter unless you're intending to tinker (which doesn't sound likely at the moment).
You can use Windows backup facility to back up your hard drive but if you've a CD or DVD writer then why not make a regular copy of "My Documents" onto a CD or DVD? I use this method and it has saved me a number of times. Your Program files can be reinstalled if you have a catastrophic failure (as you will eventually) at some time - it is your data (documents, files and in particular, digital photographs) that cannot be recreated that you need to protect.