Hi rowlandh
We recently moved to Switzerland from the UK and drove over with our cats. We had to get them pet passports which showed that they'd had a rabies injection and were microchipped and that the vaccination had worked, which required a blood test and a month's wait (this may have been due to UK re-entry requirements though - as I recall they just had to have proof of having had the jab to enter Switzerland).
When we arrived at the Swiss border I had all my paperwork ready, but the guard just checked our passports, not the cats, and waved us through!
The cats hated the journey though because we haven't ever really taken them anywhere in the car except to the vets. I guess if you're going to do it regularly though they'll get used to it. Lots of treats also helps
A quick google gave me this website
http://geneva.angloinfo.com/countrie.../pettravel.asp
which tells you about travelling to France from Switzerland - you can probably find a better link with Germany specific info.
I hope this of some use rather than me just rambling on about cats! I love them - please post pictures when you get them
maud