Good thing you were able to recover aleast your windows operating system. Getting a second hard disk just for Linux is a good idea too. however if you don't want Windows 7 in your computer at all you can format your hard drive and install Ubuntu 12.04 LTS, 64 BITs in the whole drive. I meant you will have to format your hard drive anyway if you want Windows Xp.
So my advice for you will be Save your money, dont buy a Windows Xp disk which is already obsolete ( I meant Windows Xp is like 12 years old and Microsoft does not support it anymore)
Instead install the latest Ubuntu Linux which is free and it comes already packed with the latest software you will ever need. Make sure you get the 64 Bits version which will make better use of your computer hardware. If you use it for a month and you decided you still want to go to Xp then it will be up to you.
you can download the latest Ubuntu at this link www.ubuntu.com
if you have more questions you can post them in this site and I am sure somebody will be happy to help you.
Good luck to you!