Server Side Includes...

I have a real easy question that probably has an easy answer. I'm rebuilding a site for a friend and they would like it to be more modular so I'm breaking up the sections into seperate HTML pages so I can "stack" them using server side includes. Problem is, I can't seem to get them to work. The server is IIS, not Apache, no I'm using using include file rather than virtual. I can preview them just fine in Dreamweaver but the page just shows up blank when viewed live from the web. Is there a special file I need to place on the server or in the HTML pages to enable this? What do I save a ".shtml", the index page or the seperate files that it calls too? Any help would be greatly appreciated as I've scoured the web and all the tutorials seem to be geared toward people who already know what they're doing. Again, this is really basic so just the simplest of advice is needed. Thanks.