Real? Hoax? If anyone has information, please, pass it on!
Here are some entries I found:
http://en.wikipedia.org/wiki/Argentavis - although Wikipedia isn't much of an 'authority', take these with a grain of salt...
Here's where the image came from: http://www.angelfire.com/electronic/bodhidharma/giantbirds3.html
And, here's a long history of giant birds: http://sped2work.tripod.com/evidence.html