If you create the new columns as NOT NULL with a DEFAULT constraint then the columns will be populated with whatever you put in for the DEFAULT. Like this:

USE tempdb;

GO

CREATE TABLE test (c INT NOT NULL);

GO

INSERT INTO dbo.test

(c)

VALUES

(0 -- c - int

);

GO

ALTER TABLE dbo.test

ADD create_date SMALLDATETIME NOT NULL DEFAULT '1900-01-01';

GO

SELECT

*

FROM

dbo.test AS T;

GO

DROP TABLE dbo.test;