all you need is a soundcard with line in/mic in and a cord with mini headphone plugs on each end. the cable is hard to find but you can easily make one yourself. real handy for recording 24/7, especially frequencies people don't talk much on
http://xoomer.virgilio.it/aporcino/VoxRecorder/
Can't got wrong with a good Vox recording program.
I've used this one (http://www.davee.com/scanrec/) for the last couple of years, and never had a problem. My friend who is a Sheriff's deputy swears by another program called Xcorder for his recording needs.
Here's (http://www.mediafire.com/myfiles.php?r=dkipv) my archive of stuff I've caught while monitoring. It's a slowly growing collection, given that I'm in a town of 35,000 in Wyoming and there just isn't all that much radio traffic.