You might try a query whose SQL looks something like this:
SELECT DISTINCT
[Your Table].[Your Memo Field]
FROM
[Your Table],
[Your Table] AS [Self]
WHERE
[Your Table].[Your Primary Key Field] <> [Self].[Your Primary Key Field]
AND
[Your Table].[Your Memo Field] = [Self].[Your Memo Field]
This will return the distinct values in "Your Memo Field" that occur in more
than one record in "Your Table".
This assumes your table has a single-field primary key named "Your Primary
Key Field".
