Crucial is a very reliable brand and I would click on the link supplied by bremner and order from there. It will cost you less than £30 for a very worthwhile upgrade. If you Google laptop memory replacement you will find lots of sites to show you how to do it. It is one of the easiest upgrades to perform.
No drivers to install, if you have installed the memory chips correctly the BIOS will pick it up when you boot. You can check that it is all there By right clicking Computer on your desktop then clicking on Properties.