T-Sql  update join query

Hello,  I have rows I enter into an intermediate table and perform some operations, in the final process I end up inserting  into the main table one row per  each entity defined as same firstname, lastname, storenumber and dateofbirth.  Before I do that, I need to update a field called fillename with the value of the filename based on the max dateentered field for that entity, if the fiilename field is not null.  It is possible that all rows for the entity have null for filename.

Assuming the rows of data below in my intermediate table, I want to update the filename  field all 3 to the filename field to 'blat.jpg'
FirstName LastName    DOB   StoreID  Filename DateEntered
John        Doe     10/1/1966  55         blah.jpg      10/1/2007
John       Doe         10/1/1966    55          blat.jpg      5/11/2008
John       Doe     10/1/1966    55         NULL        9/01/2008
 
Soething like this, but adding the grouping or ranking by datenetered and  adding the filename field to query:

UPDATE      mybuf
SET      filename = A.filename
FROM      tbl_MyBuffer mybuf
      INNER JOIN (SELECT FirstName,LastName,DateOfBirth, StoreID,DateEntered                
                   FROM tbl_MyBuffer   WHERE Len(isNull(fileName,'')) > 0
                     GROUP BY Firstname,Lastname,DateOfBirth,StoreID) A
            ON A.FirstName = mybuf.FirstName
            AND A.lastName = mybuf.lastName
            AND isnull(A.DateOfBirth,'') = isnull(mybuf.DateOfBirth ,'')
            AND A.StoreID = mybuf.StoreID

Since I am using SQL 2005 would this lend itself to rank() ?

Thanks!