Depends! Compaq presario 500. Created a dvd restore disc and a copy. Used the disc to successfully restore to factory settings. D: partition still intact.
Got hold of a Vista disc with service pack 1 (original OS). So I decided to go to the HP site (support) and downloaded all the drivers for my laptop.
Did a clean install and installed the drivers and was like a new machine. No HP bumff. Then got rid of the D: partition.