I can't seem to find any info via google or the search here. If I have a US XBOX, can I use it in Japan on XBOX Live? Is there any sort of region encoding for the XBOX live system?

Also, if I can use a US XBOX on XBOX Live in Japan, would I be playing against US or Japanese gamers? If I can only play Japanese gamers, then that would certainly eliminate any live-enabled US-only games. I guess I am just having a difficult time finding out information about the limitations on hardware and such. I am sure MS would love to limit the US players to the US and Japanese to Japan (just like the manufacturers do with the games themselves or DVDs) but it's not always this way in the wild wild internet....

Thanks...