Ah ah! An interesting one!

I only wish I could help ... being a fan of the Psion Organiser myself. Remember to fit a new PP3 from time to time!
But surely the program you need is in a DataPak (EPROM)? Once you have recovered it, it would be nice to save it to PC as well.
I assume you connect to the air bed via the RS-232 cable. So other methods should be possible, as long as details (of the data) are available. Is it all mentioned in the Nimbus manual?
Be sure to let us know how you get on.
For even more fun, check-out this
forum.