You lucky little bumpkin. I would love to have an 8800gtx. Id have to have a new computer but thats another story. I'm sure you will be happy with it. If I'm not mistaken it is the best card on the market.
Doable.. but not really a great idea.. as far as i know,. that will run just fine. (but i'd suggest you overclock the CPU a tad.. else it will be holding the card back.