However, for that you just need PoS tags (which is also provided by this Google thing, yes). And of course the hard part of WSD is detecting whether "bank" refers to the bank of a river, or the financial institution, or the building where the institution is located, or [you name it].

I use parse trees as a kind of "advanced language model" for when I need to replace a word in a sentence (see for example: http://www.aclweb.org/anthology/P13-1142 ), it's so much better than using just simple n-grams.