I've found a way that you may be able to play (S)NES/Genesis games on your 360. To use it, so far, you need a Vista Pc set up with a media center extender.
My method so far:
host webserver on localhost with ActiveX that launches a program
redirect go.microsoft.com to localhost VIA the hosts file
go to a website on the 360 under media center > online media > explore
right now, I have SNES windowed thru dosbox playing, accepting input off the controller.