I have been recommending Ubuntu for those new to linux. There is an amazing amount of support for the beginner and you will find most security tools compile with no or little problem.  As far as laptops go, the real key is have at least 1 gig of memory. I have had really good luck with my Acer aspire 5610, If you want to look cool at a hacker convention, then those really small ultra thins are the way to go, lol. But I hope "looking cool" at a hacker convention is not the goal, because IMHO its impossible. We are just different levels of computer nerds, but I digress.