We've got the same problems on the french forum :
i) old posts that were imported from the old 2007 french forum have been scrambled at their accentuation;
ii) all new posts that are created within the new 2008 french forum are doing fine WRT their accentuation.
So, it looks like you guys can continue to use accentuation on the new 2008 spanish forum as well.
(sorry I don't speak spanish)