VBA Excel Search and replace text....

Hi.
I need VBA-Code to search a text-string and replace it with a picture. I got a directory on my disk that contains about 1000 xls-files (every xls-file is a worbook that contains about 3 or 4 sheets), And now a need a VBA-code that han replace that litle text-string with a picture. Any one got an idea how i´m going to do this.
Thanks. NW