Sorry, I think you missed the point here, but thanks for taking the time to reply.
What we've got is a commercially available CD-ROM application. No possibility of modifying the source code.
What we want is to be able to run it in a safe way, so that no one can deliberately or inadvertently stop it's use or damage the PC (e.g. by overwriting system files).
Mike
"I can live with doubt and uncertainty and not knowing. I think it is much more interesting to live not knowing than to have answers that might be wrong." - Richard Feynman
