|"it deleted everything like drivers and stuff needed for the CPU"|
A CPU is a chip that plugs into a socket on the motherboard. The most common are made by Intel or AMD . Hardware devices (chipset, video, sound, LAN, printers, scanners, etc) need drivers, CPUs do not.
You posted absolutely nothing regarding your system specs, but if you intend to downgrade the OS from Vista to XP, make sure to search for & download all the necessary XP drivers 1st. Some drivers are very difficult to find...some may be non-existent.
You might be better off keeping Vista, repartitioning the HDD, then installing XP on the 2nd partition. That will create a Vista/XP dual boot setup.
How to dual boot Vista and XP (with Vista installed first) -- the step-by-step guide with screenshots