I know vbulletin.com has the members area so that the password can't be saved (at least on my browser it won't LOL)...the only thing I can find on it is to add autocomplete="off" to the input code like so:
<input type="password" name="password" id="password"
autocomplete="off" />
I don't know if this is the only part that disables the password being saved, but worth a try
Hope it helps anyway lol
Lissa