There is not a way to get a completely free working version of Dreamweaver, any version, legally.
With each iteration of a product, they add new features, but the core of dreamweaver stays the same (web editor), so you can learn on any version...but be aware that the newer versions add features to make your job easier. But also, Adobe has released video and white papers on the new features, so you won't be too lost. And you can always do a youtube search on "Dreamweaver CSx new features" (where "x" is the version of dreamweaver).