Its a while since I did this but its roughly as follows.
Download a program called Audacity (an audio recording setup) and install it. Put your DVD in the reader and set the system to record. You should see the soundtrack appear as two 'waves', one above the other as the dvd plays. When its done, normalise it, save the recording as a 'wav.' file and then burn it to a CD. Obviously it follows that you can just record the bits you want and save them as seperate tracks rather than recording the whole soundtrack. You can boost bass and other levels if you think fit.
You'll have to set the input to the right one (either 'line in' or 'stereo mix' ) if my memory serves, and you'll also have to adjust recording levels etc; best just record a couple of minutes at a time and fiddle with the settings until you get the hang of it.
Its straightforward enough once you have the thing in front of you (he says)!
Have fun.