What O/S are we talking about?
Keep in mind that years of use of a Windows system accumulates a lot of debris, some of which you probably don't want to retain. In the end everyone needs a real Windows CD sooner or later.
If you want to preserve this as it is do a google search for free imaging software, or check out Acronis True Image or Ghost if you are willing to pay. (Although if you ar ewilling to pat, you may just want to invest in a Windows CD.)