Hi Shirley,

You may have to use a standard paper size (as far as Word is concerned, and
increase the Right Margin so that you end up with equal margins on your
actual paper size.

The right margin will need to be

   WPW - (WPW - APW) - LM

where WPW is paper width specified in Word, APW is actual paper width, LM is
left margin setting.

Then centre align the text.

Please post any further questions or followup to the newsgroups for the
benefit of others who may be interested.  Unsolicited questions forwarded
directly to me will only be answered on a paid consulting basis.
Hope this helps
Doug Robbins - Word MVP