Hi mimmiepmp!
You have a 2-year window for booking with the world passport collection (aka Interval Internation, or II on the boards here). It isn't difficult to do, as you just call MS with your request. It does cost a $95 booking fee though.
If you are flexible about which resorts you stay in and/or date ranges you can go, most people can get what they want.
Hawaiian bookings are the only exception . . . where you have to be really flexible as most people using II want Hawaii (the demand is very high). Actually, most members want the top-end Hawaiian resorts - and if you're willing to consider some that aren't so high-end, it will also increase your chances of getting to Hawaii.
I am told that 50% or more members do get their Hawaiian II requests if they book early (say at the 2 year window) and wait . . . as most of these timeshares (Hawaiian or not) open up at the 1 year advance window, with
DVC'ers getting in at the 5-7 month advance window being common.
As was explained to me in a town hall meeting at OKW last year . . .
In the end, you are effectively trading your DVC timeshare for someone else's timeshare. They put in their request for a trade to DVC through theirs, surrendering their timeshare . . . and we DVCers put in just a request (along with the deposit). None of your points are actually allocated to this trade until a match is made - and you can cancel your request at any time before the match is made, getting your $95 deposit back.
If you have to cancel such a reservation (assuming you got your match), your points used for the match go into "reservation points" (which means that you have to use them for an II match again at some point).
Hope that helps a bit!