Netbooks Laptop

I got a laptop (ASUS EEE PC) about 9 months ago, however it is running terribly and I don’t know why. How can I restore it to how it was when I purchased the product? I basically want to wipe the hard drive, and just have Windows XP and internet explorer on there. I have very little computer knowledge, but I know enough that i can uninstall / install where necessary. Likewise, I have no idea what it means to ‘flash’ a PC.
The laptop is this one…

http://www.carphonewarehouse.com/broadband/laptops/buy/ASUS-LAPTOP

Thanks in advance,
Alex.