First, you have to be a Gold Member of II. You reserve your Marriott week and then contact the Cruise Exchange department. You tell them which unit you want to deposit and which cruise(s) you would like to go on, which category, etc. Then, II gets 7 days to determine how much $$ they are going to give you towards your cruise. You pay the rest. So there is no chance you will get 2 rooms, unless you want to pay full for the second and the difference for the first.
A lot of people here on TUG will recommend to stay away from a cruise exchange because you won't get a decent value. I have no idea what sort of value II currently provides. I did a cruise exchange shortly after they offered it, back in Jan 2005. We booked it with II in about April of 2004.
I deposited a good Platinum week at Fairway Villas (NJ) and received just under $1000 towards my cruise. So it cost us a little less then $1000 to cover the difference. That was for a Promenade view on the highest floor that overlooked the promenade on the Royal Carribean Adventure of the Seas for a Southern Carribean 7 day cruise.
You have the opportunity to just back out of it when II tells you how much $$ they plan to give you. But like I said, you need the Gold Membership just to start the process. Good luck.
