I understand that your are not satisfied with Vista like many others.
To go safely from Vista to XP is a lot of work, I hope that your ready for it.
Here is how and good luck
What you should do before Windows XP installation
When moving from Vista to XP there are things you should do before formatting the pc! Please save all your personal files like Music, Pictures, Documents and useful Software etc... You can save all these stuffs on your other partition D: or on an external HDD/USB flash disk.
Creating Installation CD/DVD
When downgrading to XP... the vista drivers won't usually work! So it's really important for you to download all your drivers... The most important drivers you will need: Sound card, Graphic adapter, Chipset, LAN and WIFI.
You can use some driver scanning software:
This is a tip to learn about Everest: https://ccm.net/faq/ 2604 everest identify your hardware devices and drivers
You can even download all your XP drivers from your motherboard manufacturer's website!
If you already have a Vista license, there's no need to purchase another license.
Never use copies of Windows XP and even modified versions Like LSD, Gold, Ultimate and the Amit XP SP 3 version. You can have problems with your devices and malfunctioning system files!
SATA Hard drives
SATA Hard drives are sometimes not identified by windows XP so you must have the SATA drivers for your Hard drive.
* https://ccm.net/faq/ 2544 installing windows xp on a sata hard drive
* https://ccm.net/faq/ 2370 downgrading from windows vista to windows xp hdd s ata not reco
Some PCs have a tattoo mark. The tattoo may prevent the installation of Windows other than that originally installed and can prevent the resettlement system, ie, if one day you want to reset the PC by default if you come from purchase.
Dualboot XP / Vista
Have both Windows and be able to choose between them at startup, but it can be done in relation to tattooing, it can touch and corrupt.
It is also possible to buy a hard drive and install XP on it. So, simply change the hard drive when you want to change Windows. If you really want to use XP and Vista to keep the original, it can be practical.