So you're gonna make your own 1x4 or 1x5 or 2x3 keypad?
Thats Exactly what i am trying to do.
If it's a keyboard that is less than say 8 - 10 years old it is almost certainly of the membrane switch type. Taking them apart and using only some of the keys is very very difficult one of the reasons being that thee is nothing to solder wires to.
I teared up the Keyboard and here is its internal
http://img214.imageshack.us/img214/1/img0048mb.jpg
I think its not possible to solder it as you said, so i gave up the idea of making a keyboard of mine out of it.