Well unfortunately, sound seems to be one of the areas laptops still lack. Most, if not all general laptops have integrated sound (i.e of the motherboard, not of a seperate dedicated sound card/device).. and generally the sound isn't great. So when you go onto customisable dealers like Dell, you have no customisation options for the sound card, since well.. there isn't one. Of course, the sound will still be pretty good from most integrated cards (especially if you're able to get your hands on some nForce2 mobos), but don't expect it to be as good as say, sound generated from Sound Blaster Live!/Audigy cards etc. Also I'm assuming that you'll be using headphones.
For all your other activities, you won't be requiring much power. So I estimate you could get a reasonably good laptop suiting that criteria for around $1400 - $2500.