Sounds so simple. But. There is a jack receptacle (and my 1/8" line jack fits) on the back of my computer with a symbol that indicates sumpn' or other. It's not a headphone logo but shows a thing being inserted into some kind of receptacle. Nothing happens when I plug them together.

(Am I correct in thinking you are saying that the other line - the one that comes with the Mini Disc unit (the USB, I think) is the one that gets inserted into the jack?   That's the one I'm talking about here.)

The 1/8" line (which I just bought) inserts into the Mini Disc and has a corresponding ho' in the computer. When I plug it in, the computer beeps and says 'Found New Hardware' and then says 'Your new hardware is installed and ready to go."

And then what? (A case of virtual beer (your choice of brand) to the ones who lead me through this!)