Z brush is wonderful, and has lots of bells and whistles, but Mudbox is much easier to learn. They are both wonderful programs and I am sure you will love them. I wrote a book on transfering the traditional process to digital means. It is called ]Digital Sculpting with Mudbox: Essential Tools and techniques for artists.
The one thing I love about the book is there is an entire chapter about getting the object out of the computer. And check out this video that I created on how the program works.
if the you tube video does not come up on the forum you can find it at http://www.youtube.com/user/sculptor.../0/78rxEAicgpM
Sometimes I like to use both programs just to help me get my sketches for my client. Here are some links on this
Using Poser, Daz and Zbrush
there are others on this blog about these tools and processes. Hope this helps.