I don't think you can do this while keeping the "Data Form" visible,
because it is a "modal" dialog box, but assuming it is a Word .doc data
source, you should be able to:
a. click "View Source". This opens the .doc as an ordinary Word
document. It should contain a Word table with one column for each field.
b. You should also see the "Database" toolbar as a floating toolbar.
If not, try View->Toolbars and check the database toolbar.
c. Select the LastName column and click the button with AZ and a down
arrow.
d. Save the document. You can close it if you want.
e. click in your mail merge main document.
f. in the data Merge Manager, click the Data Source->Edit Data Source icon
Even if your mail merge data source is not actually in Word table format
(e.g. if it has more columns than Word tables allow) you should be able
to click in the column you want to sort on and use that database menu to
sort the records.
Peter Jamieson
http://tips.pjmsn.me.uk