Highlighting duplicate values in a column
 

Our department is involved in project managing office moves. The
moving department is given an excel 2002 spreadsheet and they fill out
the names of the people moving (column A) along with their extension
number (column B). I would like it to pop up a message if an
extension number is entered and is a duplicate of one already entered,
giving the person's name it's duplicated with.

Any help would be gratefully received

TIA

Rather than pop up a message, how about if you set the conditional
formatting for the cells in column B to highlight if a duplicate
extension is entered?

Set conditional formatting to "formula is" and use this formula
(altered, of course, to fit your data):
=COUNTIF($B$2:$B$17,B2)1

Then set it to highlight in red or yellow to indicate a duplicate.