I was there in '08.
When you arrive you get assigned an agent - although it's unclear how easy it is to do it without - probably fine. We were only allowed a permit to stay in one place, not to visit other islands, so we did it using the local boats instead (but we did have someone to stay onboard for us).
I know that it's a big deal destination
for lots of people, and that I'm sure I won't put you off, but it is an absolute hole of a place.
Everything is a cynical ploy to extract money
from you and they look after the place really badly, while bleating on about how hard it is to survive on bottled water
. I was there during a 2 hour rainstorm that completely filled our dinghy
with water, I was ashore at the time and watched as gallons and gallons of drinkable water flowed off the roofs, into the street and then into the sea - no gutters!
There are far, far nicer island groups you can visit in the Pacific. I remember the Marqueses very fondly indeed. Especially Hiva Oa and Ta'ha (sp?).