I would very strongly recommend the wonderful Audacity, a great little sound editing program that I've used for putting 30 second sound files on websites. You don't need to be a music editing genius to work it out and best of all, it's absolutely free. Sorry if I sound like they're paying me to advertise (they're not), but I love it.
You just record a whole track to it, which it will represent as a sound wave. Adjust the size of the timescale until you're happy, then just click and drag across the excerpt you want. You can set points on the soundwave to create a nice graceful fade-out too. Then just save your excerpt as a separate file, in either wav or mp3 format (mp3 unless you're going to want to re-edit - a wav is full quality, but about 10 times the file size), and Bob's your uncle.
The latest beta version is 1.3.7, but if you want full instructions, go for 1.2.6. Download it free here:
http://audacity.sourceforge.net/