I was just rereading a blog post by Euan Garden about SQL Server's history and he refers to the fact that you can read a chapter about the history in the Inside SQL Server books. In the rewrite of the book for SQL Server 2005, when we split the book into four parts, we had to remove the history chapter, so I took the chapter from the SQL Server 2000 book and made it available online. When reading Euan's post, I realized that most people, including Euan himself, probably didn't know it was available so I decided to make that information a little more public.
You can find the chapter here.
http://insidesqlserver.com/companion/History%20of%20SQL%20Server.pdf
Have fun!
~Kalen