You can add anything to your library from your external hard drive on iTunes, Windows Media, winamp, etc. and listen to it from it easily. Just gotta make sure your portable hard drive is turned on each time you're listening to music. It seems you don't do much music listening on your PC anyway, so if it's simply for the purposes of participating in this thread, you can just do it that way.
02/04 - Machine Head
04/08 - At the Gates