I'll second Vertable's recommendation for ASUS, if you want to go the off-the-shelf laptop route. As the only laptop manufacturer in the world who also manufactures their own motherboards and video cards, ASUS consistently offers more bang for the buck than anybody else. I absolutely love my G70 (quite outside your price range, though).
The G series is their gaming line, but their N series machines also work well for SL. The N's aren't typically quite as good as G's, since the graphics cards are midrange instead of high end, but they're a damned sight better than what you've got now. There are several that would fit within your budget.
That said, the unfortunate truth is that in order to keep the costs down in most sub-$1500 machines, laptop makers have been making the screen resolution worse and worse and worse with each new generation, as they put in better CPU's and graphics cards. Apparently, they figure people who buy cheap laptops don't care about how much they can see, as opposed to how fast they can see it. We're now at the point where most laptops in the $1000 range come with resolutions of 1366x768, which in my opinion, is pathetic. If you plan on doing any texture work, forget it. That's barely enough pixels to see a 512x512 at full resolution, once you factor in the couple hundred pixels needed for the GUI of your paint program.
If you can up your budget to about $1700, the game totally changes. Check this out:
http://www.malibal.com/boutique/pc/configurePrd.asp?idproduct=84Malibal is awesome. For just $1772 (after you up the screen resolution to 1920x1080, increase the memory to 4GB instead of 2, and put in a 7200 RPM hard drive instead of the stock 5400), you get one of the fastest 15" notebooks on the planet. It should last you a good many years before you'll need to upgrade it.
All that said, if that $1000 figure is firm, then I'll echo Briana's recommendation. Get a desktop. For a grand, you can put together a really decent machine. Cheap laptops are a very poor investment by comparison. You'll just have to spend that same $1000 again on a new laptop in a year or two when the current one can't keep up anymore. The desktop, on the other hand, will likely just need a new graphics card in three or four years, which will probably cost you just a couple hundred bucks, and then you're good for the next two years or so before the CPU is no longer up to snuff.
So, if you think in terms of the next six years, which is about how long you can get out of a sufficiently maintained desktop, you'd be looking at $3000 for poorly performing laptops, or $1200 for a well performing desktop. Is it worth the additional $1800 to you to be able to sit on the couch with a slower machine in your lap? I say sit in a chair, spend less, and enjoy the nice fast desktop.