I just came across Geses Bow Staff. Is it usable? Is so, where do I find the string? I would like to be able to use it a soon as possible.

Well here it goes. You need to go to the Asylum and go to the second floor and it is in the room with the three golems in a chest.

Yeah, sorry to say you can't use it "As soon as possible" simply because you really can't use it until chapter 6 when you are able to return to have it made. Of course by then the game is pretty much under wraps. Just like wuth the Crom Faeyr and the SIlver. All the good stuff just simply comes to late, that is unless you put off doing any of the side quests and went straight to the funny farm.