Mass Updates In SQL Server

Does anyone know what the best way to do mass updates in SQL server is? I am currently using the methodology suggested in this article

http://www.tek-tips.com/faqs.cfm?fid=3141

But the article is assuming that once I update a field it is going to have a value that is NOT NULL. So I can loop through and update the rows that have a NOT NULL value. But my updated rows do contain NULL values, in this case what is the best way to go about this???

***************************************
Here is my code. I want to avoid using Upd_flag becos
after the following code runs I need to reset that flag
before I run my next query
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--Set rowcount to 50000 to limit number of inserts per batch
Set rowcount 50000

--Declare variable for row count
Declare @rc int
Set @rc=50000

While @rc=50000
Begin

Begin Transaction

--Use tablockx and holdlock to obtain and hold
--an immediate exclusive table lock. This usually
--speeds the insert because only one lock is needed.


update t_PGBA_DTL With (tablockx, holdlock)
SET t_PGBA_DTL.procedur = A.[Proc code],
t_PGBA_DTL.Upd_flag = 1
FROM t_PGBA_DTL
INNER JOIN CPT_HCPCS_I9_PROC_CODES A
ON t_PGBA_DTL.PROC_CD
= A.[Proc code]
WHERE t_PGBA_DTL.Upd_flag = 0


--Get number of rows updated
--Process will continue until less than 50000
Select @rc=@@rowcount

--Commit the transaction
Commit
End