Steps
1.Can you ping the SQL Server, and can you connect using SQL Connection not NT?
2.To use NT Authentication, you must be added as part of an NT group or a NT login in SQL Server, and given permissions to do this. Check this out as next step.
3.Check you client tools configuration on you box and have tcp/ip and multi-protocol selected.
4.Does you NT domain use DNS, if not you might have to add the IP address to a lmhosts file