I want to reinstall Windows XP Professional my own.

If you want to do so...you can follow these procedure:

1. If you don't have the CD/DVD, Buy your genuine MS Windows XP Professional SP3 and Windows Office 2007 (I can't suggest you the price, it may be vary).
2. Write down all Computer Device type (you will need it when installing device driver). To find it, right click on your "my computer" icon on your desktop and click "manage". Locate "Device Manager" and write down all device that listed here. But do not to worry about it, most of well known device are included in Windows Driver out of the box. For some computer, the driver could be found on the CD that shipped with the computer when you've purchased it.
3. Copy all of your data (i.e in "My Documents") into your external Hard Disk or other backup device such as DVD or CD.
4. Make sure your computer's boot priority set to "boot from cd" as first priority. You can set it in BIOS option.
   
5. boot your computer, and follow instruction from Windows CD (it will be easy thought, it almost clear for every instruction).
6. After the installation finished, you might be needed to install device driver.
7. Install Office 2007 and follow the instruction (believe me, it's easy!)
8. Copy back all of your data from your external harddisk to your new "My Document"
9. It's all done