Don't go with InDesign. It's (obviously) a great app, but just to make a newsletter you'd be wasting a ton of money. I use Pages for newsletter-ish activities and it's a very easy-to-use app that (for the most part) doesn't involve a lot of formatting mess and complication. Save it as PDF if you want them to only be able to read it, but if you want them to be able to edit it... it has a decent Microsoft Word export feature, so if you have Word you could export it and then tweak it in Word to unscrew whatever the export screwed up. Oh, and don't listen to all of the negative criticism about Pages - an inDesign killer it is not, and a Word killer it is not, and it is far from perfect but I use it frequently and find it takes much less energy to make something look good in Pages compared to Word. Think of Pages as iMovie and inDesign as Final Cut Pro. Or Garageband vs. Logic.