I have a Excel list made of 6 columns.
Records are added to that list daily.

I want to be able to create a helper column that will show an "X" next to a
row that has 2 records, let's say on column A and C ONLY, identical to those
in previous rows.

Example:
A B C D E
John 06/18/08 $ 590.00 256 A
Jack 06/19/08 $ 700.00 300 C
Mark 06/18/08 $ 590.00 256 A
Miles 06/19/08 $1,1190.00 300 C
Jack 06/18/08 $ 700.00 256 A...............X
(Identical records on Col A AND C than row 2
Lee 06/19/08 $1,1190.00 300 C

Any help or pointer will be gratefully appreciated