Do you like macs at all? An older mac will suite you just fine, and you should find one with those specs and pricing. It may sound like a cliche but macs are great for graphic design. Personally I think the new macs aren't built for the artist anymore, just the general population, but the ones from like 2007-early 2009 are great. Check out Mac Of All Trades for a good used mac: http://www.macofalltrades.com/
They don't seem to have many laptops as of now, but hold out, they get them in like crazy.
If you don't like Macs, I would go with a Dell Studio or some sort of HP. Those are usually quite reliable and work really well. The HP Tx2 is an awesome tablet but it's small, has a weak graphic card, and is ATI. I oved mine when I had it. I drew everywhere on it. If you want a forum dedicated to helping you find the right laptop, check out here: http://www.notebookreview.com/