I must let you folks know that I eventually found exactly what I needed with a program called "AJC Directory Synchroniser". It cost around $30 or so, is simple to use and is does exactly what it says on the side of the tin.
I downloaded a trial copy and admit I had a problem setting it up, but a quick email to the product support folks (who found the problem was me!) an it works just fine.
I have simply copied the entire C drive to an external Maxtor hard drive and set the new program to keep everything synchronised. It does its business at whatever times you care to program it to, and for me, it is a fantastic bit of kit. Well worth a look.
STL