Daniel Shaughnessy wants iTunes and Windows Media Player to see the music on his external USB hard drive.
This can be done, but there are two caveats: You have to tell these programs that a particular folder on the external drive should be part of their music "library." And you have accept occasional error messages when the drive isn't plugged in and the program can't find the music you want to play.
Here's how to add the appropriate folder to the library:
In Windows Media Player 11, with the external drive plugged in, press F3. Click Advanced Options, then the Add button below the list of folders. It's all pretty obvious from there.
In iTunes 8, select File, then Add Folder to Library (in iTunes 9 this appears simply as "Add to Library"). Select the folder from the resulting Browse For Folder box. If the external hard drive is your main source of music, you can select it as the primary library source by going into iTunes Preferences, clicking on Advanced and hitting "Change" next to the iTunes Media Folder location. From here, you can also allow iTunes to reorganise your music collection or automatically update the hard drive with any music you add directly to iTunes. If you choose to do this, however, you must make sure your external hard drive is connected whenever iTunes is open.