This is because once you completely remove the operating system from your computer, then it becomes a Basic Input Output System otherwise known as BIOS. This is when you would use those recovery discs to reinstall windows. It takes 17 cds because the cds only have about 700mb of storage capacity while the dvds have about 4.37gb of storage capacity. That means that each dvd amounts to about 6.4 times the amount of a cd. You need about three or four dvd in order to create recovery discs because of all the information that windows vista carries.
Now when you say that you used a program back in xp, you must have been referring to system restore, not full restore. System restore restores your computer to an earlier date at some point in time. Full restore or Full system restore completely removes the operating system in which case you would need recovery discs.
Edited by gr8joel, 13 March 2009 - 04:39 PM.