Thanks for your help. In the end, I used mkpasswd (as included with expect) to do this. It was only after the whole thing was up and running that I found out about chpasswd.
I was thinking that since quite a number of people I know start using Linux/Debian at home, and then "fertilize" their work environment, we tend to find these problems. This could be a great question to put in FAQ. Again, thanks for your help, Jose -- Jose L Gomez Dans PhD student Radar & Communications Group Department of Electronic Engineering University of Sheffield UK