I don't imagine you'd get away with an actual emulation, not in actionscript at any rate.
Having said that, there is a javascript 6502 emulator page out there somewhere. I just can't imagine someone writing a 680x0 emulator in a language like that
The above is a quote from Karlos in another thread...
You have to wonder, could a C64 emulator be written in Javascript? If it could, then you could run it on an iPhone happily (or any webkit device)... with the new HTML5 tags, I think one could write something really quite reasonable!