Thank you for the advice. Some good stuff.
I back up my pen drive to two external hard drives at weekly intervals. Not perfect, I do agree. None of my personal files are too important. I'm more concerned about easy and quick recovery of my the PC to its pre-virus state if it becomes infected, without spending hours installing software from scratch.
On the Win 7 PC, I've already experimented with the above recommended combination of boot DVD and 'system image' (i.e. Windows plus all personal software) on an external hard drive. I can transfer the image onto a
completely blank internal hard drive (I've been experimenting with a spare drive, identical make and size to the original). However, I can't get the image onto yet another spare internal hard drive (also identical make and size to the original) with Windows 7 installed from the supplied OEM disk. Not sure why there's a problem there, which is why I'm here looking for less puzzling recovery software, which is what Acr**is used to be before the terrible Win7 version.
Am I doing something wrong in the last case?