Probably anything will work - I don't recall AutoCAD requiring anything super high end. Heck, IIRC it even runs fine on integrated graphics. People at work were running it on Dell Latitude D600 series notebooks with 1GB RAM, 1.6GHz Pentium M CPUs and integrated graphics.
As for direct suggestions, how about a Dell Vostro 1500?
Here's the link. The "Dell Deal" for $599 with free shipping (limited time offer) comes with a 15.4" widescreen, Core 2 Duo CPU, 2GB RAM, 160GB hard drive, 128MB Geforce 8400GS video. Can even increase video to a 256MB 8600GT for $100 more.