*quirks jaw*
I was told that, except for the differences in configurations from one cartridge to another (and there was some 16 normal board types), the process wasn't too tough. Just take a board of the right type (that being sometimes difficult; I understand some of the types can get a little rare, and finding a cartridge you don't mind destroying can be hard among those board types or whatever...) and unsolder the EPROM's.
The hardest part, so I was told, was making an EPROM writer to connect to your computer. Friend of mine had an EPROM writer, he says, but he also says it bwoke, and he'd have to make another, just for his own purposes.
So, tell me about the proveness of Flash roms...