in addition to what tamia said, you can also back up your data by using an external hard drive. there's actually a related thread about that here in
www.testfreaks.com/forum. go to the computer hardware category
in any case...yeah, you can use an external hard drive. the price depends on the capacity of the hard drive. so far i think the largest capacity available these days is 320 GB.
in order for you to back up your data, all you need to do is plug that external hard drive to your laptop via USB cable (this comes free with your purchase of external hard drive). it's a plug and play scheme, really. don't forget to format the hard drive though before you use it!