Um, if you wanted an HP ipac, why didn't you buy an HP ipac? You bought a music player and expected to read random files on it? Forget the hardware issues with letting people drag and drop music willie-nillie all over a music player and expect it to work perfectly, but expecting it to let you display random documents doesn't make any sense. We are on our second ipac. They cost $700 a piece (at least, might have been euros...) and they crash all of the time, but you can move any old files you want back and forth to it. You can even edit them.
People who think they should be able to drag and drop their music completely miss the point that player's desktop software is adding meta data that is making your life as a mobile music listener much more pleasant. Knowing that the files will always be just so on the player makes the hardware designerss lives much much easier so that they can concentrate on more important interface issues. Basic things like pre-adjusted volume, equalizer settings, favorite lists, bookmarking, album song order... forget album covers and silly stuff like that, I can't imagine what using a player that was forced to treat the music as a random pile would be like. Ick.