Converting 9-digit zip codes to 5-digit zip codes

I have an Excel file (using Excel 2007) which has a column devoted to zip codes. I have it formatted as "Custom" - "Zip Code" (not Zip + 4). The entries in the file are generated from imported information from an external file. The file comes in as a CSV file. I convert it to an Excel file. Here's the problem....some of the zip codes have the 9-digit format while some of the zip codes have the 5-digit format. I would like to make all the zip codes in the column "5-digit" which means I need to drop the "dashes" and the last four digits from all the 9-digit zips. I've tried everything I know, but nothing seems to work. Last night, I went down a column of 500+ zips and manually corrected them. This just doesn't work. I posted this issue earlier....got a response called "zip code fixer.xls", but I don't know how it works. I would appreciate anyone giving me some hints on how to collapse all these 9-digit zips into 5-digit zips. Thanks very much. WDP

Why not just use =Left(A1,5), copied down. If you know that you always want the 5 digit zip, then the 5 digit ones will remain the same, and the 9 digit ones will be truncated.

-Bob