You could export it to Comma Separated Values file and then just pull the column that you want out of Excel (or other spreadsheet program).
OR
If the view allows it, you can customise some views.
From the View menu choose "Customise this View".
(at least that's where it is in Notes 6.5)
This allows you to show / hide columns.
Then hide all except the column you want and then do an export to text file.
If you have a mail file, you should see the customise option in the Inbox view to give you an idea what you're looking for.