I'm using a Hypersonic GX6 that's a couple of years old. 3.2gig P4 with a gig of DDR400 RAM, 1600x1200 LCD screen, one 60gig 7200 RPM internal system drive with another internal 100 gig 7200 drive for video. It works absolutely great, although battery life is a bit short.
I'm lovin my Toshiba DuoCore Centrino that is a huge improvement in preview smoothness and framerate (about 50%) over my AMD Athlon 3200. It's possible you'd be better off buying one with dedicated video display, however, for a couple 100 more,