The ipac really wasn't designed for this kind of thing at all.
What it is looking to get is a series of simple on/off signals. nintendo and sega controllers have a bunch of electronics to encode the on/off infomation into a form that makes sense to your sega / nintendo.
So no, you can't just lop the end off the controller cable and screw the wires into your ipac.
you kight be able to do this by gutting all the electronics from the nintendo / sega controlllers and turing all the contacts into simple on/off switches which bypass the internal electronics all togehter. This would mean that your ipac could understand the input but the controller would then be useless for anything but connection to an ipac.
To be honest the ipac is the wrong solution for htis problem. there are a huge number of usb addaptors that allow you to plug all kinds of crazy controllers into a USB port on your PC.
this place has some - buy one of those
http://www.blackchopper.com/store.phpdisclaimer: I have never bought anything from the guys above and so I can't recomend them. don't come crying to me if they rip you off.