I think you're trying to transcribe the music, aren't you? It can be really tough sometimes to get parts that are buried in the background, but your computer can be a tremendous help.

There are several "wave editing" programs available that can make this easier. I have a few pro-level things I use for tough cases, but the thing I use most when transcribing is the cheapo "Creative Wave Studio" that came free with a Soundblaster card I bought years ago. First you have to record the piece to your hard drive as a .wav file, then you can use Wave Studio to slow it down to half-speed (it also drops the music an octave when you play back half-speed).

Sometimes this is all the help you need. Two other programs I use are Sound Forge and DC Art32, although these aren't cheap and and you have to have a little understanding of audio to make the most of them.

Another excellent program is "Musician's CD Player" from Roni Software -- I tried the demo, it's absolutely the best of the programs that let you slow down music without altering the pitch. Other software that does this introduces nasty artifacts and impulse noise, but the output is very clean from Musician's CD player.

One I haven't tried, but see a lot about is "Cooledit", haven't tried it so can't comment but you should have a look at it.

Demos are available for all this stuff (except "Wave Studio" which you probably already have if you have a Soundblaster card). Sorry I don't have url's handy but a web search should turn this stuff up pretty quickly.