Reading Amazon kindle books on Windows XP, Vista and 7 is easy peasy. Log into your Amazon account and download the software: Amazon.com or Amazon.co.uk.
This is essentially the "app" for Windows.
When you buy kindle books off the Amazon website, you can have them wirelessly delivered to this or any other device that you own.
If you download a book to one device it will be in the Archives on the other devices so you can simply reload it to an alternative gadget at no additional cost. Happy days.
This is how you can read kindle books on iPhone, iPad or Mac.