The OE works with all 3.x versions, and there is a 2.x version available. While the 2.0 OE wasn't released until 3.5, as far as I know it should work just fine with any 3.x versions. I know the upgrade was seamless on a big 3.3 installation one of our clients is running.
I have not personally installed it on any 2.x sites and can't comment, but according to the docs it should work.
