If you are purchasing a laptop, you probably want to look for a system with hardware specifications comparable to, or better than, the Dell Latitude E6540 example system shown in the PDF below. Basically these specifications are:
If the laptop model you've chosen can support an add-in video card, you may wish to add that also.
Laptops are available in a number of size, though 14 inch and 15inch are the most common. These tend to have the best balance between weight, mobility, and performance. There are also 17-inch models which are nice to work on because of the size of their display, but are cumbersome if you have to carry them around.
You'll also want to think about what kind of warranty to buy for your laptop. Laptops lead harsher lives, and are usually harder and more expensive to repair than desktops. Many laptops on UK's Dell Educational sites come with a three-year on-site warranty. If you configure a system from Dell's full catalogue, you'll need to choose the length of the warranty. As a rule, the life span of a laptop is typically three years so keep that in mind when deciding how much to spend on the warranty.
Finally, if you buy a laptop, you should consider adding accidental damage coverage to the normal warranty if it's not included, and is available. This is the warranty that typically cover the display, and damage from falls or liquid spills.
The following sample configuration is based on UK's departmental standard configurations:
You might also want to check http://www.dell.com/coupons for any special deals that Dell might be offering on laptops. Code shown on this page can be used when you checkout to increase your savings.
Operating System Note:
Depending on the which Microsoft Windows-based computer you purchase, it will come with either Windows 7 or Windows 8. Though Windows 8 has become the dominant version of Windows for new consumer models, some enterprise level systems (such as the example Latitude E6540 above) still come with Windows 7. You should experience no issues using either version of the OS.
Microsoft is no longer releasing security updates for Windows XP. If your computer is running Windows XP, you should update the OS as soon as possible or purchase a new computer.