This is a really good overview, with examples, of how to use SubVersion for writing, web projects, etc.
I personally use and recommend SubVersion, largely because it support explicit “move this file” “this file is now obsolete” and “add these all together” semantics. The Using SubVersion for Writers posting is an excellent reminder of just how helpful and simple SubVersion is, even for small non-technical writing projects.
Installing on MacOS ‘Leopard’ is trivial: it’s already there. To add a GUI, use either SCPlugin to add a SubVersion menu to Finder, or SubVersion Scripts (here’s a great screencast). It is easy to install SubVersion on earlier versions of OSX, as well.
For Windows, I like TortoiseSVN. On Solaris and Linux (Red Hat, Ubuntu), I tend to use the command line.
For reference material, see the “Red Bean book” SubVersion.