I have spoken to a few computer / IT buffs over the years and they told me that DELL are the only brand name / pre-built PC they would buy. I assume that applies to their lap-tops. Other than that they would only advise a hand built machine from an Independent. I have a TIME lap-top and touch wood it is trouble free (apart from a dodgy CD/DVD ROM drive that will not read CD-R disks.)
Go for at least 512Mb of RAM though 1GB would be better. Most new laptops have quite powerful processors, 2.4 + so you will be fine there. For using CAD consider a wide-screen. As much screen “real-estate” as possible helps with the eyes. Try to get a DVD writer for backing up and a nice big hard drive.
if your lookin for something to deal with three dimensional cad and open gl you need to throw in a pretty decent graphics card too…bear in mind a good graphics card will set you back a few hundred euros
check out the forum http://www.boards.ie…they are excellent at giving their advice on the best parts to buy re cad etc if you are assembling it yourself….