Thanks guys. My question was answered very well indeed. I assume rims dont matter but hubs do. And naturally I would have gotten the cassette so they could be swapped easily.
Now my problem is how to get these bontrager oem hubs?
I use the same cassette on both wheels Road/Off Road --- takes me an extra 2 minutes to switch them out (W/Tools of course)..
a huge problem that you'll find if you use 2 different cassettes is that the chain will get more used to the cassette that you put more miles in(Road Tires in my case) then when you go off roading your highest gears will start skipping BADDDDD... and no derrailleur adjusting will fix that..
So instead of buying a new cassette for the extra set of wheels, i'd take that money and buy the tools to remove the cassette if you dont already have them.
my 2 cents... (i've been burned before 2 hrs away from home @ Santos)