Sega Dreamcast: get a gameshark if you are interested in 3d imports like Giant Gram 2000 or Frame Gride...but a utopia boot disc would be fine if you are just trying to boot up 2d fighters or something. Th reason for getting the gameshark is that it supports VGA while the utopia boot disc does not.
Super Nintendo: a bbq lighter and a steak knife is how I modded mine, but it could be messy if you burn the lid. I heated the knife and cut out the plastic pieces in the snes. I am sure there is a cleaner way....maybe some small metal snips or something. The only difference on the super nintendo is the slots in the back of the US carts. If you look into your US super nintendo through the game slot you can see the two little plastic things that stick out on the back side that slide into the slots on the game cartridge. The problem I ran into was that I couldn't get all the plastic out and now I have to wedge a piect of card paper in front of the game to get the game to not lean forwards. But, if you can get all of those two pieces out, everything should be fine. It sounds stupid, but it works and I can play those crappy snes import ports all day long,lol.
Or you could try and make the slots on the cart and leave your system alone like the guy above me said. Either way, there is no modding needed for either of those systems if you don't mind swapping discs with the DC or making your snes games or system imperfect. My snes was old and not mint looking anyway, so I didn't mind.
Sorry, I don't have my genesis or sega CD anymore so I haven't gone that route yet w/ imports.
anyway, good luck!
<small>[ July 29, 2003, 08:09 PM: Message edited by: NGT ]</small>