[i]A Prologue is a part of the story writtn in the point of view of the story (think of it as chapter zero!)
A preface is an introduction written by the author in the voice of the author
A Foreword is an introduction to the story written by someone else and preceeds the preface[/i]
A preface is usually written by the author, but a foreword can be written by anybody, including the author.
I've always defined preface as being directed more towards the story being related or the topic being presented, while a foreword is far more encompassing and may include references to other issues such as reasons for writing the book.
In almost every case, you should get rid of this throat-clearing stuff on an e-book. Recast it as an Afterword. When the prospective reader opens your book on the Look Inside sample, you have got to hook him within a very few pages, so don't waste them on copyright information, acknowledgements, and all that jazz.
Generally a preface is an intro to the whole text (usually for non-fiction), and a prologue is a sort of "scene setter" sometimes employed in fiction--less popular these days.
Before you include either, though, make sure you have a good reason! If you're just thanking your loved ones and Sparky the dog, I'd suggest putting it as endmatter.
I have an author now with a whistle-blower book; his preface states plainly that it's a work of non-fiction and that there are no anonymous sources. Given the nature of his material, that's info we want up front (also, he stated it nice and briefly).
There's no hard-and-fast rule, but do ask yourself what you're trying to accomplish with frontmatter, and if a prologue or preface (or intro) is really the best way.
I agree with Notjohn. Get rid of the preface, prologue, foreword, etc. It's all just one more excuse for a potential reader NOT to buy your book. This is especially true for fiction. Just tell your story.