I pulled this from the BOL

"...a nonlogged bulk copy can be performed if all of these conditions are met:

The database option select into/bulkcopy is set to true using sp_dboption.
The target table is not being replicated.
The TABLOCK hint is specified. For more information, see Controlling the Locking Behavior.
Additionally, if the table has any indexes, then there should be no existing rows in the table to perform a nonlogged bulk copy. The combination of indexes and existing rows of data cause the bulk copy operation to be logged.

Any bulk copy into Microsoft® SQL Server™ that does not meet these conditions is logged. "

The last item is the stickler. If there's data in the table, you'll have to drop the indexes.

-Mike