QUOTE (Franz Kölliker @ Jan 28 2010, 10:09 PM)

we'd like to use these sticks later in school. So the pupils got their own "carry away" OS.
Or do you think a BartPE/chrome OS/Knoppix installation would be easier/more practically?
The main issue, as I see it is the licensing.
Unless you have a very special License Agreement with Microsoft, the "distribution" of sticks to pupils will be a breach of the Eula, apart from legal considerations, not morally the best thing in the world to teach in a school.

Same applies to BartPE, or any Windows based PE's, and to the actual apps you mentioned (Office - meaning Microsoft Office and Adobe products)
I don't think that Chrome has the features you are probably wanting the OS to have.
Knoppix is a concrete possibility, but there are a number of other Linux based distro's that may be more suitable.
In any case, you will need to rephrase:
QUOTE
The system should be running on every usb-bootable computer.
to
QUOTE
The system should be running on most usb-bootable computer.
There isn't AFAIK
ANY OS "portable enough" to be 100% guaranteed to work on
every USB bootable computer, unless you use a Virtual Machine based approach, which would slow down matters considerably.
jaclaz