You have a couple of options. You can either wipe Vista off completely and start fresh, or you can
install XP alongside Vista.
Also, when buying a copy of XP, you can either buy a Full Retail copy of XP or an
OEM copy of XP. The main difference is price and licensing. The OEM version is cheaper than the Retail version by over $100, but it can only be installed on one computer. The retail full version costs more, but it can be installed on another computer if your current computer ever dies. A Retail version cannot be installed on two computers at the same time though.
BMR777