Before installing Windows XP, I recommend you change the resolution of the display. Right-click on your desktop, click Screen resolution and select a smaller resolution:
If you are not satisfied, check the article provided by Microsoft in order to downgrade your operating system. In this article you will have all the necessary instructions. Unfortunately, you can't download any package for Windows XP because the operating system is no longer supported by Microsoft. This is the main reason why I don't recommend you install Windows XP. However, if you really want Windows XP, you will need to purchase an CD from Amazon, eBay or other similar websites.