Karl,
If you are looking to develop Newsletters to send via email or post up to
your Website you would use an html editor. This being a Microsoft post I will
suggest Microsoft Expression Web Designer, or Front Page, however, you can
design these documents in Publisher as well.
In Publisher select Web Sites, scroll to the bottom (in Publisher 2007 beta)
select Web 600 x 4608 px but never wider than 760 as there are still some
machines set to 800 x 600 resolution. Then you can begin being creative.
My company develops these types of documents for our customers using an html
editor, save as Stationary, (the images have to be stored and directed to via
online server) and send using Microsoft Outlook.
Hope this is the information you are looking for.
Jerry