So the device has a red/white output for output to a stereo source?
If so, you'll need something like this:
Basically its a lead that has 2 phono connections and a lead that goes to a 3.5mm connector, to plug up to a Line In or Microphone jack on your sound card in the computer
Or find a lead that has two phono's, and no 3.5mm, and connect something like this to it:
Ignore where the link goes to. Its just an example
Once you have the cables sorted out, all you need is some software, and you don't have to look any further than this:
Audacity is a FREE Open source recorder, which is capable of pretty much anything. Simply plug the cables up, run that program, set to record from a certain input, and hit play on the deck and record in Audacity.
OUTPUTTING AS AN MP3 RATHER THAN WAVE:
If you want to output as an MP3 file within Audacity, you can go into Edit/Preferences/Audio Files, and there is an option to find a LAME encoder to allow you to export as an MP3.
Download the Lame codec here:
The first link if your running off Windows.
You then unzip this, and within Audacity, find this Lame.dll plugin by clicking on Find Library, and double clicking on the file to allow Audacity to see it, and then, all will be sorted out.
Then you can just set bitrates (i.e 128-320kbps), and your then ready to export out the files afterwards too!
I hope this helps.