best practice for private intranet area?

I need to create a simple intranet. My current thinking is that this need be just a blog, which includes upload tools, accessible only to people in my "intranet" group. What is the best practice for setting this up that won't get in the way of setting up other, public blogs, or other controlled access areas? Is this what "organic groups" is best for? Is there some way of defining a node as "intranet1", say, and then letting only people who are "intranet" users" have access to it?

I'm still very much a newbie, so if this has already been covered reasonably and I have just missed it, feel free to point me to specific documentation.

Thanks.