If disk-space is not an issue for you, you can create a flat data file from SQL Server and use FastLoad to load it to Teradata. Your second option can be using TPT with data-direct to connect to SQL Server directly and bringing the data to Teradata.
If you are currently outputting 12million rows are sinle inserts then Fastload/Multiload is definatley an option. Your scripts can call the utilities in a similar manner to BTEQ, hoever you will need to output the data file from you batch script before doing so (you will also need to create a definition script) - see the Utilities manuals for advice as to how to access/use the different loading utilities.
Post an further questions and I will try to aid you in this migration.