I don’t have any idea about NT, I am proficient on 2000,2003 and XP.
As for your new job, please tell me what you are going to be doing. Do you know what O/S you will be using? Are you going to have to set up the network yourself?
As far as certifications go, they are nice, but as I have found, nothing subsitutes for hands-on experience. I am sure you know more than a certification test will tell you.
I can recommend someone who may be able to answer your NT question, just tell him I referred you. You can email him at firstname.lastname@example.org.