Notebook or Desktop?
For CAD you'll want a dual core processor and at least 2gb of ram. Storage is cheap now so you can actually get up to 500gb without stretching your budget out too far.
Which autocad software will you be using. Land Desktop 2005? 06? 07?
As far as graphics goes, it all depends on how much your rendering and what exactly you are doing with CAD.
For a OK priced HP, the HP nx9420 comes pretty loaded, with a Intel Core2 Duo (2.16ghz),
2.00GB Ram,
and a 100GB Hard drive(not sure on exact size, will have to look, as it has a recovery partition). It's a 15.4" widescreen as well.