From the post what I understand is you are loading the data of txt file to a table using bcp.
for datatime you can put getdate() as default value and for username column put (suser_sname()) as default value in the table. It would give you both current username and also date.
CREATE TABLE [dbo].[Table1] (
[col1] [int] NOT NULL ,
[col2] [varchar] (50)NOT NULL ,
[col3] [datetime] NOT NULL
) ON [PRIMARY]
ALTER TABLE [dbo].[Table1] WITH NOCHECK ADD
CONSTRAINT [DF_Table1_col2] DEFAULT (suser_sname()) FOR [col2],
CONSTRAINT [DF_Table1_col3] DEFAULT (getdate()) FOR [col3]