PFUNK:
Did you define the table zip field before or after you entered zip data into the table?
If it was defined before any data was entered, then the entire 5 digit would have been stored. But if it was initially defined as text, then redefined as number and redefined again as text, you would have lost the leading zeros.
If this is a one-time correction, I've found that a better way to handle this kind of update is to use the services of Excel, instead of writing code that will only be used once.
Open a blank Excel spredsheet, and your table in the database. Format the first two columns in Excel to Text.
Then in your db table select the entire zip column and paste it into the first spreadsheet column. It will also put the column header in the first row.
In the first row of the second spreadsheet column thype the following equation:
=If(Len(Trim(A2))=4,"0" & A2,A2)
Copy this equation all the way down to the end of your first column's data. Select the entire 2nd column and copy it. Then do a Paste Special ... Values right over itself.
Now copy the second column (be sure the first row has the identical table column name) and select the zip column in your db table and paste. Access will ask you to confirm the paste. Check that the number of records you are pasting is the same as the number of records in the table.
If you make a mistake, you still have the original data in the first column of the spreadsheet. (It might also be a good idea to save the spreadsheet after you've imported the zip code column.)
HTH,
Vic