for those who ask, vnc viewer works great on local network, the interface answers acceptably. in fact, it's a good way to surf on the internet by having the maemo5 browser improvement and the n810 bigger screen. but it's not really useful in a local network (assuming you have a pc or a laptop).
But if you can do it by using the n900 as a localhost for the n810, it will means you can do it everywhere, and that will sounds great...