amd64 is what Debian calls x86_64. The two are identical. It’s just a misnomer on the part of the Debian folks. I’m running it on an Intel Core 2 Duo as we speak–it is not specific to AMD processors. (And, as far as I know, nobody uses ia64 boxes for hosting. They’re too darned expensive.)
Note that it isn’t officially supported yet, as I’m still testing and working on the actual install process–I don’t know if it will actually work, as is. It’ll be ready by this evening. I will announce support on the front page in the News section and in the News forum as soon as it is ready for mass consumption.