This is a problem. You see, the CD key is basically what you're purchasing when you buy Windows. And every version of Windows comes with a CD key. If it did not, then the version you purchased was stolen, or you stole the actual copy itself.
Now then, there is no actual way to postpone the Validation without registering the copy of Windows with an illegal crack. As it is illegal, we wont discuss this bit.
You basically have several options:
1) Assuming that you purchased your version of Windows from a licensed dealer, etc, etc, you find the CD key printed on the case, the disk, or the box.
2) Assuming that you purchased a copy, but you do not have a CD key: Return your copy to the person you purchased it from and then repurchase it from a valid dealer.
3) Assuming you downloaded a copy: Buy the real version.
4) Alternative: Use Ubuntu with no support for Windows games.