You won't need anything specific other than a cable.
I looked up the stereo system you have, but I can't tell if it has an auxillary output on it. I'll assume it doesn't, so you'll need a 1/8" stereo cable to connect the headphone jack of the Sony to the Aux input of your soundcard. You'll have to adjust the volume of your Sony down quite a bit since the headphone jack puts out a slightly amplified signal and you'll want to let the PC do most of the amplification of the signal.
Anyway, connect the two, and go into your Windows sound mixer (double click the little speaker in your taskbar) and enable the aux input of the soundcard for recording. You do that by going to options/properties and checking the "recording" option then OK. Your aux in will either be labled "Aux" or "Line In" depending on your soundcard. You may have both, so you'll have to try it out.
The biggest thing you'll have to get is a recording program. You can go to http://www.download.com
and search for "record wav" or something similar. You'll have to sift through the results to find one that's truly free. Most are either save disabled or have a 60 second limit on saved files unless you purchase. But there are quite a few that are very cheap to buy.
Once you have a recording program, you'll simply play your tapes through the Sony (you should hear the tape through your PC speakers) and click record on your recording program. Only thing left is to get your levels right on the Sony and the aux input on the PC.