From my XP experience, I decided to build my own machine about a year ago to eliminate the enforced use of (then) Vista and all the other cr*p that the manufacturers insist on loading new machines with. Bits bought, put together and the XP rescue disc from my old machine (now dismantled, cannibalised and out of use) inserted. It booted and informed me that it was formatting my (brand new) hard drive. It then proceeded to install XP which was validated with the aid of the serial number on the label on the old computer case. (Tip - from this forum - always use the telephone option to revaildate XP)
I have used this disc to rescue several computers using XP when a repair is not feasable it always reformats the sectors which contain the operating system before commencing a fresh installation.
P.P.