There are some newsletter templates in the Office Template Gallery at http://office.microsoft.com/templates/default.aspx?. Use them with caution
(perhaps only for inspiration), as they're heavily text box-dependent and
really work against Word. Publisher is generally a much more suitable
application for a newspaper-like newsletter (that is, one that has articles
that begin on page 1 and "jump" to an inside page), but if you are creating
a newsletter that's pretty much sequential, with perhaps just a few text
boxes or frames for sidebars or a TOC, you can do it in Word well enough.
Just keep in mind that Word is designed for word processing (continuous text
flow) rather than page layout.