My boss gave me the C860 and told me I can do whatever I wnt with it as he find no use for it.

I have read about the different roms I can use and I am ready to try (I'll start with Open Zaurus).
I do have one question, is there any way for me to revert to the original condition, as I am currenly on
the Japanese OS and if ever my boss would want it back, he'll want it in japanese.

Are there any back ups of the original roms or is it illegal question?