You're thinking too hard. It's a lot simpler than that.

Keep in mind that the timeline doesn't contain actual cilps or files. What it contains is references to the files on your drive. Whatever you do on the timeline, the original files are still there untouched on the drive ready to be used again. If you want to use the sound from one clip with another clip, import the first clip on the timeline, then click on the video portion and delete it. The sound portion will remain on the timeline. The clip itself on your drive isn't altered; it still retains both the audio and video, but only the audio portion will be used in your project.

To load a clilp into the media pool, click on the first button at the top of the media pool window to bring up a browsing dialog box, find the clip on the drive, and double-click on it. Alternatively, click on the Explorer tab and search your drive that way.

If you really do want to create a file that has only the audio portion (for example, if you captured a clip from your camera just to get the sound, and don't want the video part filling up your drive), then load that clip onto the timeline by itself, Make Movie, and select .WAV as the file type. This will create a WAV file with the sound only. You may then delete the original .AVI file if you're sure you don't need it anymore. This method can also allow you to create a "soundtrack" audio only file of your entire project if you wish.