It won't work..Asus doesn't use standard MXM pin sorting in their PCB's. You'll need to use either Dell or Clevo, I recommend Dell due to plug and play and Dell supported drivers. You should grab a 560m!
gtx 560m is freaking $$$$. I think i'll just stick with the gtx 260m. The rest of the system isn't that great, just an i7 720qm, 4gb ddr 1333, ect ect..... a gtx 560m would be bottlenecked by that processor
The asus is the same slot I believe but the card is a different size, people have put in 7970M cards in the asus.
Otherwise cards are best found on ebay usually or the members market back over at NBR, dell do sell them but they wont be cheap and they usually will only sell you cards officially compatible with the machine you have.