Macro to `populate empty cells in a region

I'm using Excel 2003, and have data that looks something like this:

       A                B               C                D                    E                   F
2  Last ame     FirstName    Middle      CorrectLast   CorrectFirst       CorrectMiddle
3   Agell           Robert           L.			
4   Araham       Angel            E.	          Araham          Angel                E
5   Aman          Peter				
6   Aler             Donald          B.	          Aler                Donald              B
7   Ainge          Jody				
8   Albrom        George         W.           Albrom           George              W
9   Almano       Ronald                         Almano           Ronald	
10  Aller           Sylvia				
11  Alma          Raymond       N.			
12  Alyn           Janet             H.

There can be many more rows. What I'd like to do is build a macro that will
go through a selected region - to include an area such as this - and populate the empty cells in columns D, E and F with the appropriate columns in A, B and C.
So, an empty cell in CorrectLast would mean that Correctlast would receive LastName from the same row, CorrectFirst woudl receive FirstName from that row and CorrectMiddle would receive Middle from that row. In this example, D3 would hold "Agell", E3 would hold "Robert" and F3 would hold "L"

If somebody could point me in th right direction, I'd be very grateful.
Thank you for your help.