So I did somethign pretty dumb and cut the cable by accident. I 'assume' I need to unscrew the three screws on the bototm of the shifter in order to get at recabling it and get a cablewitha special knob on the end from my LBS?
I've had em break off inside before. I've been able to get it out with a pointy instrument. You just have to dig at the end with the cable stop. I'm not exactly sure of your model, but often times disassembling a rapid fire shifter isn't a good idea, unless you are pretty good.
I am not familiar with the shifter, but usually you work the shifter, with some tension on the cable, till it is in the small cog/ring position. Then you should be able to push the cable out through the shifter. Put the new cable in through the same hole. The Shimano website will have diagrams/instructions for your particular model.