Just for information. I have several computers & external hard disks, and managed to get several different versions of the same databases. I was looking for ages for software that would enable me to merge these into a single up-to-date database, and finally I found the ideal solution. It's called "Beyond Compare" (http://www.scootersoftware.com/) and comes in pay and free versions. The free one did everything I needed. There must be lots of other people out there with the same need and I can recommend this without reservation.

Thanks, works great!