My answer's long, so I want to say up front: I think you want OpenOffice Writer (I use v2.4, haven't tried 3.0 yet).
I've used Word with equation editor and LaTeX heavily in the past and OpenOffice Writer
more recently. I used the former two while writing my thesis.
LaTeX may still have advantages in quality of the output and in the ability to use text-based version control, but they're sharply diminished by OO Writer at this point.
Microsoft with equation editor, even the most recent versions, seems very weak still.
What I like about OpenOffice is that you can use the equation formatting mechanisms
in a mode where the window is split between the document you're writing and another
area where you can type very LaTeX-like formatting instructions. One of the big
strengths of LaTeX is that you get to type up something like $x \in S$ for "x is an element of S". OO Writer lets you do this and see the result.
Back when I wrote my thesis, LaTeX was preferable to Word with Eqn. Editor because of the length of my document (over 200 pages), the quality of the results, and the ease of specifying equations. LaTeX does have a disadvantage in simplicity of use that is made more acute by OO Writer.
That said, I'm sure I'd use OO Writer for conference to journal length articles (~8-15 pages v. ~15-40 pages) and also for shorter work. For thesis-length work, I'm not sure which I'd end up using: Word never worked so well for me on longer matter; I suspect OO Writer is better behaved but I don't have enough experience of it to make a firm judgement.