On my Dell it's hidden in the Windows\Options folder. Look for *.cab files (Cabinet files)
When you added any new hardware did you get the "Insert your Windows CD...." messages followed immediately by the machine actually going ahead and loading the software / drivers etc for the hardware anyway? So whatever you do don't do as I did and format the drive!! - A long time and a lot of trouble ago on another machine. If you did then Windoze is hidden on your HD.
Compare the *.cab files with the contents of your CD.