- change the Evaluation Edition (120 day limit) to the Retail Edition
- change the Development Edition (10 user limit) to the Retail Edition
To determine if an installation is the evaluation version, see IsTrial, which is a freeware utility.
A lot of people have been caught in the catch-22 of carelessly using the evalution setup diskettes with the retail version of NT. Although the CD is the full retail version, you will still get the 120-evaluation life-time. See Microsoft's Q173507: Evaluation Period Expires on Non-Evaluation Copy of Windows NT
TechRepublic has published a manual process to upgrade from the Eval version of NT to the commercial version. I haven't tried it but I have reviewed the documents and the process documented should work. Let me know if you have success or failure if you use this document.
Check out Microsoft's kb article Q173507: Evaluation Period Expires on Non-Evaluation Copy of Windows NT