Look for a computer with a powerful processor probably a core i3, i5 or i7. The next thing is a high processor speed, RAM capacity like 4gb and a big hard disc capacity probably 500gb. You will also need to consider whether you will be carrying you laptop around on a frequent basis so you should go for a lighter machine. Another factor to put into consideration is whether you will be using your laptop in places where electricity is a problem then that way you will need one with a long battery life.
Go to Cnet.com and look at reviews. PC Magazine has reviews. Go to Best Buy and Staples to try out brands. You may want to make sure the keys have a back light. Leo LaPorte has a podcast on tech and the Wall Street Journal has a great tech column.