Will this be a good card and will it work with my power supply. I plan on playing WoW and dual screening (one for WoW) and one for internet.
P.S.--Since its Black Friday/Cyber Monday is here, which would be the best day to buy from TigerDirect/Newegg and Im also looking for a 1920x1080 monitor. I want the total amount of the two to equal no more than $350.
Why are you wanting the gtx460 when you already have an HD5770? Your current card will do what you want.
But to answer your question, a gtx460 will let you use both monitors, and since WoW does favor Nvidia, it will perform better than what you have. Your power supply has the wattage needed, assuming it's of reasonable quality.
That's a good card for a good price (after rebate). If you can afford it, the 1gb version will perform a little bit better at 1920x1080 resolution. Those cards are about $170-$180 after rebate, but they come with a free copy of HAWX 2.