I'm interested in buying a laptop for school as well as for work. What are the pros and cons for buying a new or a used machine.

The drawbacks of buying a used laptop are mainly that you don't know how many hours of use that they have had--and no indication of how knocked-around it might have been. Batteries and LCD backlights have a finite lifespan, and both are expensive. I have seen horror stories, even on this site, of people buying a machine that seems fine for a day or so--then crashes-and-burns.

Add to this the fact that a used machine is likely to be "behind the curve" with respect to performance and installed software--and the recent drop in prices ($850 will buy a decent machine these days) indicates that, unless you get a hellaciously low price on a used one, a new one is actually a better value. Also: new machine, new-machine warranty. Of course, your mileage may vary.

I would agree here with Michael.
I have an HP which is just 1.5 years old. But my battery and lcd is already dead.
There are basically 3 classes of latops .
1) The desktop replacements. These are cheap , generally AMD or Celeron. But are heavy and have lesser battery life. About US $ 750 and above.
2) The light ones - These are generally centrino's. Expensive but light , long battery life and so on. Above $1500
3) The extreme performance one - These beat desktops in performance but are very expensive. Ideal for gammers and graphics people.

I would sugest go for 1 if you do not have money. Else take 2.

Regards
Amar