Dell's are pretty cheap and very easy to fix. Keep in mind the average computer lifespan is 4 years. I used to have one, now I have a macbook pro.
I've seen lots of people in exams that have netbooks, and they seem to love them. I am picky when it comes to the size of the screen and having to "squint" at it. Keyboard size is important too.
If you have some *cough* scholarship money, or are looking to get a nice computer, buying a nice high-end mac is a great investment -- especially if you purchase the total care protection plan they have. If you ever have problems you just take your computer to a mac store and they fix it (or try to) on the spot -- Dell you have to schedule an appointment, and yeah it is nice to have the technician come to you, sometimes you just need to get things fixed quickly.
Betasteve is right, you must use bootcamp to boot up softest. No you dont HAVE to use a computer for exams, but from the amount of words I type in a 3 hour exam writing doesn't seem feasible -- especially the way exams are scored. But I know people who swear by bluebooks and have done well sans computer.
Keep your options open but make an educated decision. You don't want to spend low, only to have problems (which will always arise with technology) just to have to spend more.