windows 2000 professional

I HAD WINDOW NT 4.0 SERVER IN A LAB
WITH 24 WINDOW NT WORKSTATIONS AS A PART
OF A DOMAIN IS IT POSSIBLE TO UPGRADE WINDOWS NT WORKSTAION TO WINDOWS 2000 PROFESSIONAL AND SERVER STILL
BE OF WINDOW NT 4.0 , BECAUSE AS I TRY TO
MAKE IT A PART OF DOMAIN IT GIVES MESSAGE
DOMAIN NAME NOT VALID. IF THE ANSWER IS NO
YOU GET 5 POINTS IF ANSWER IS YES AND WITH THE CORRECT SOLUTION U GET 150 POINTS