Start with a blog. I highly recommend getting some hosting(I use http://www.dreamhost.com/), and setting up wordpress on it. Don't limit yourself to just using a blog and put it in a different directory. http://rcthink.com/blog for example. If there is nothing in the home directory(http://rcthink.com/) just have it redirect to /blog for now. That way you are not restricted in any way later on if you want to start a full on website.

Get into blogging, and figure out everything there is to know about that. Then when it comes time to expand, you will have the knowledge and a decent configuration to do that.

The biggest thing to keep in mind is NOT changing your URLs for your blog posts. Once you've written all those blog posts and have a lot of traffic, you don't want to throw that all away by changing all your posts URL's. Try and set it up so that you can keep them as they are as long as you use that site. If you really do need to change it, there are ways to redirect the pages so that you don't lose the PageRank.

Cheers, Ross

Starting a blog is definitely the way to go. It's a significantly easier publishing platform than the alternatives and enables you to build up an audience interested in your future ebook. A more static website is far less likely to have consistent readership.