At that price point, dude, you're gettting a Dell. I think they were offering a 15-inch Vostro this week for $550: 1.4 GHz Core 2 Duo, 2 GB memory, 160 GB drive. The same computer with a 250 GB drive and two-year warranty for $730.
I'm tempted to advise you to spend $900 on a refurb MacBook, despite having almost none of what you asked for. But I work at a university, and I've observed that after a year or so of ownership, virtually the only users still happy with their notebooks are Apple and ThinkPad owners. Two Dell users came in yesterday, and both of them referred to their notebooks as pieces of [excrement]. My father has a $750ish Dell notebook which I advised him to buy, back when he thought anything would be 'good enough'. Now every week he asks me if he can upgrade to a MacBook Pro. I dearly want one myself, but I always tell him my honest opinion -- which is that he really doesn't need to spend $2000+ on a notebook. Though perhaps I might steer him towards a MacBook when his Inspiron finally gives up the ghost.
When working out your costs, please budget enough for at least a two-year warranty,
especially if you're buying a cheaper notebook. It's fairly difficult for the average user to repair a notebook computer, and third-party costs are prohibitive. You'll definitely want external backup storage, whether it's another computer or an external hard drive, so if you haven't got one already, plan on buying an external drive within a few months.
Other than brand and physical design (size, weight, aesthetics), your biggest decision will probably be: integrated or discrete graphics. Under $1000 it may be very difficult to avoid Intel inside (GMA X3100 or whatever integrated graphics they're offering now), though you may be able to find GeForce 8400GM or the like. Ah, this past week there was a
deal for a $600 Vostro with GeForce 8600M GT! For audio, plan on buying good budget speakers (external) to set up in your room.