I heard a new Xbox console is coming out. Will it be able to play Xbox360 games and use Xbox live??

The answer is no. At least, not anytime soon. Mainly because Microsoft đã đưa ý kiến themselves that they are not currently working on their tiếp theo console. Here's what President Robbie Bach had to say about this "nextbox":

“Just coming up with something that’s faster and prettier isn’t going to be sufficient. The life cycle for this generation of consoles — and I’m not just talking about Xbox, I’d include Wii and PS3 as well — is probably going to be a little longer than trước đó generations.”

Quote taken from "Mercury News.com".

The Xbox 720 is expected to come out in mid 2011-12. It's highly likely it will support backwards compatibility and Xbox Live.

I don't see why not