No, it will not void the warranty.
To get the OEM Xenons, you're looking at a quite a bit of money.
You can try the MB dealership... or try
www.bekkers.com, or
www.************************, and there are others too, I'm sure they'll chime in.
Yes you can do it yourself... it's not too easy, as I've heard, but it doesn't absolutely require a mechanic.
Good luck!