look for a computer that's got the following.
-at least a 2.5ghz dual-core processor - athlon or intel. MUST be dual-core.
-at least two gigs of ram for xp, four for vista. more the better.
-7200rpm hard drive (it makes a BIG difference), as much space as you think you'll need. 250's pretty good if you don't do something stupid like leave movies on it or something.
-chill pad (this is an aftermarket thing get a chill pad for 20$ and extend your computer's life for a year or two).
your big concern is audio, then - word processing is very easy for any computer to do, so you just want raw processing power. you don't need some special audio card or anything - just straight-line computational speed.
is there a specific reason you want a laptop? desktops are always better than laptops in terms of cost, they'll always outpace a laptop's performance, and since you'll be at college you'll be near enough to your system to use it. buy a shitty laptop off of ebay for fifty dollars (like i did...xubuntu ran like a dream on it) and put the cash into your desktop. no one actually NEEDS to compose on the go, anyways, the only reason to have a nice laptop is if you fly a lot. a netbook or an old craptop is all you need for taking notes in class =)