Go
here to see how to hack the controllers.
It is a 9-wire cable that you need
1. up
2. down
3. left
4. right
5. select
6. start
7. A
8. B
9. Ground
Find some Sega Genesis controllers on ebay and cut them up or buy an extension for sega genesis controllers.
BIG NOTE!!
If you are using NesterDC SE the way you "reset" the game your playing to go to the main menu is different. You press the dreamcasts left analog and and start buttons to bring up an in-game menu were you can choose to go to main menu.
There are two ways to wire this extra connection.
Using the reset button on the nes, run a wire to ground, left analog and start on the dreamcast pad.
or wire another button on the nes controller to two buttons on the dreamcast pad. An easy one would be wire the select button to X on the dreamcast and the have a small wire going from the left analog to the wire used on the select button. That way to get to the in-game menu all you have to do is press select and start at the same time. I do not believe any games require you to press both buttons at the same time please tell me if I am wrong because this is how I plan on doing mine.
Here is another
picture of soldering points for the dreamcast.
Just in case you haven't been here. This
site has a full tutorial on modding the nes w/ a dreamcast.
If you have any more questions please ask.