IMO don't buy dell, I've had nothing but problems with them I know some people are lucky but I know alot of people that aren't so lucky lol
Personally I'd go with a hp laptop, portability, and you can get a good bit of stuff for your money.
As for running linux, i'd get slax, its bootable so when you want linux just pop the cd in and boot up linux, when you want windows take the cd out.