I'm using Zbrush 4R4 (I need to download the latest 4R7 version it seems as it has some new features which sound useful) for the actual sculpting. It's not cheap as a single user licence comes in a $795. However Pixolgic is releasing a cheaper core version of the software with a more limited feature set. There are loads of online tutorials (some free, some not) and plenty of teaching books for all skill levels available.
To prepare for a 3d print you need to use a number of inbuilt plugins. One of which, decimation master, massively reduces the amount of polygons while keeping the detail, which makes it easier for the 3d printers by keeping the file size manageable! The other is called, 3d print exporter and converts the zbrush file into a format for 3d printing such as .stl or .obj (I use .stl), this plugin also allows you to set the dimensions for your print, specifically height as Zbrush doesn't actually have any way to set the physical dimensions within the software itself. I then normally check over the .stl file in a software called netfabb which allows me to adjust a few things and make repairs to the mesh such as closing any small holes to keep the mesh water tight.