You have NetBios Name Resolution problems. Are you running WINS? If you are make sure both your NT4 and your Win2k DCs register with WINS. If you dont have WINS you can use an LMHOSTS file to load up the nbt cache on both systems. Also make sureyou have NetBios over TCP/IP enabled on the Win2K DC. This is found on the WINS tab, under the advanced TCP/IP settings.
External trusts made with NT4 domain can be made if the the Win2K domain is running in EITHER mixed or native.
Answer 1 is incorrect. NT4 cant use Kerberos and the ADS client does not give you this functionality and also does not do anything to help with establishing trusts. The ADS clients or for NT4, and Win9x clients being used in a Win2K domain.