I'm not going to comment much on cpu/HD/memory specs cuz I think that everything else you really need to know has been said (in a nutshell.... just make the cpu big, get at least a gig of ram and make sure you have a good vid card). but having used AutoCAD for years now with school and less so in work, I can tell you first and foremost, one of the other most important things to make sure not to skimp on is the size of the screen you buy on your laptop. before entering grad school this fall i bought myself the Asus z71v not for this reason, but it was definately a selling point. The res is 1680x1050 and in a CAD or any sort of 3d modeling/drafting/photoshop application it is simple to say that screen real estate is key. the bigger the better and there's no arguing about that one. get him something widescreen.
If you're going Dell, I know a bunch of friends with their 9300s and its 17 in. widescreen and they are all very happy with it, it is actually a nice laptop for our uses and I would say is very similar to mine (unfortunately the 17 in part of it makes it a bit larger than I would really like though). My Asus is wonderful..... no complaints at all here (and btw, the graphics module is not upgradeable, not that its impossible but asus hasnt' and most likely wont upgrade it).
when it comes to quadro or anything else I have honestly not seen any real difference. having taken projects of my own from my sans-quadro comp to another with it I couldn't care less as to which I run it on just because many of them either equally ran fine or equally ran like ass. my best advise would just be to save your money and spend it on other upgrades which would probably be more beneficial (cpu/ram/HD or something with better video)