Help needed with a search formula

Dear Forum,

I'm trying to solve the following issue. Any help would be greatly appreciated.

Last Update Latest Project
01/07/2009 ENC
02/07/2009 RX
03/07/2009 X MUX
01/07/2009 ENC
02/07/2009 RX
03/07/2009 X Rx
01/07/2009 ENC
02/07/2009 RX
03/07/2009 X Enc


Description:

Three columns - Last Update, Latest and Project.
I want the Latest column to automatically insert "X", against each of the latest project entry.

I'm pretty sure I need to do this with an array formula. Which I would prefer instead of a macro.

Cheers

JediDad