Dude.. the same happened to me few days back.. n900 got totally wet.. it would switch on but the touchscreen and speakers were not workin..
dont try to switch on the phone for atleast 2 days.. take of the battery and put in a bowl of rice.. thats what i did and and its working flawlessly remember do not switch on the phone till its totally dry
rice or hot air only makes the air around the n900 a bit dryer (ie less saturated in water).
It just makes the process slightly faster.
but if your phone hasn't dried in four days, I would recommend diassembly and cleaning, as was mentionned earlier in the thread. if it still doesn't work, then it's dead (you cannot revert oxydation damage).
dont try to switch on the phone for atleast 2 days.. take of the battery and put in a bowl of rice.. thats what i did and and its working flawlessly