Microsoft Windows License Code

Have you checked on TechNet for the information?

One item you might want to read is
The Windows 98 Resource Kit

There may be a registry change which can do this, I don't know..

I do believe however, that if you turn off the computer when are asked to enter the License Key, when the computer is turned on again, it will go to that screen again.

If you are installing the OS, so that you enter in a license key to continue with the installation, and you want them to be forced to enter their own License Key when they turn on their computer for the first time, there is a registry setting which holds what the license key is (you see it when you view system under control panel).. I can't remember where it is, I'll have a look... a quick way to find it would be to check your license key, open regedit, and search for that string..