How many CD?

I got DELL XPS desktop two years ago, and am not sure how many CD I am supposed getting to format the desktop and reinstall it again when needed. I have gotten one CD. I really can't remember how many CD I got when receiving it. I got Drivers and Utilities for reinstalling Dell XPS Desktop Software. Is that one or am I missing other CD?

I found the rest of CD and looks like Windows Vista Home Premium 64 BIT SP1 CD is the one to install to renew the desktop from fresh start?

Thanks.

By conincidence I have a Dell XPS. I have one DVD for drivers etc and one to reinstall. The reinstall DVD is not necessary because there is a restore partition that you can resintall as if you had the DVD.
By pressing a certain F key during boot, you can restore the factory specs, just as though you had the DVD.