Help with Windows7 on new hard drive

Hello, my pc has recently been undertaking extreme issues with it's hard drive and I believe it is time to buy a new one; a WD Black. Obviously with a new hard drive I will need a copy of Windows 7 but I don't understand the difference between these two and I am unsure of which one to get:

http://www.amazon.co.uk/Microsoft-Wi...ords=windows+7

&

http://www.amazon.co.uk/Microsoft-Wi...ords=windows+7

Windows 7 already came installed on my HP p6-2260ea and I'm not sure if that will cause any interference. Thanks for reading! :)

Regards