>What should I look for?
Well you need to think what you are going to do with it.
If you are going to carry it around a lot you need to think about the weight of the laptop, and the battery life.
If it is NOT going to be carried around then weight and battery life are less important and you can perhaps go for a bigger screen for example.
The main technical things to look for are power of the CPU (processor), amount of memory (at least 1Gb), size of hard disk (at least 80Gb), and version of Windows Vista (try to go for Vista Home Premium rather than Vista Home Basic)
Try to go for a good make (Toshiba, Dell, Sony, Compaq, HP, Lenovo, and so on), avoid the cheap no-name makes that PC World and Currys will try to sell you (Packard Bell, Advent etc)
Maybe buy a magazine like What Laptop
http://www.whatlaptop.co.uk/