Active Directory FQDN/Netbios Name Same

My question is when I went to upgrade an existing NT4 domain with the netbios domain name of something.org to active directory it did not like the something.org as the netbios domain name because it gave me the error that the dns domain name was already in use. Can I not have the same netbios domain of something.org and a AD domain of something.org? Is there some special trick that needs to take place in order to make this happen, or do I need to change the netbios domain name to not be equalto the AD FQDN? Any assistance would be appreciated.