No, Mudbox won't do rigging but it does have translation tools (move, rotate and such)...at least not version 1.0.  There's talk of an update to it though.  Here's the thing:

If you've never had any experience with digital sculpting tools (Silo, Blender, ZBrush, Mudbox) but you have modeling experience, you'd probably be comfortable with Mudbox's interface. It's way easy to jump into Mudbox and make something because of how the interface works.

If you have had experience with digital sculpting tools, than it gets a bit tricky. ZBrush3 can offer quite the advantage, since you get a program that can be used to texture your model as well as simply be used to sculpt it.  ZBrush3 does have a psuedo rig system that relies of ZSpheres but to be honest, I don't care for it much. So ZBrush has a bit of an advantage if you have prior experience, as the learning curve in that scenario would be minimal and centered more on the texturing side of things.

Both programs allow for hyper detail well into the tens of millions of polys, with ZBrush3 claiming to allow up to a billion (though if you really need that many I pity you).

So try out both. There's no demo of ZBrush 3 (this may change during or after Siggraph) but there is one of Mudbox.  YOu can get a demo of and old ZBrush but things have changed a little in ZBrush 3, enough so that the demo of ZBrush wouldn't help.

Mudbox comes in two flavors (ie. prices) : Commercial and Non-commercial, while Zbrush comes only in Commercial.  So check them out. Go visit the forums for both and get a feel for what people complain about each and what people like about each. This may also help you to decide.

I wanted Mudbox but needed to get one of the two programs as soon as possible, so I purchased ZBrush since the commercial version was cheaper.  I think Mudbox is on sale at the moment (or maybe that was a special one week thing last week)  15$% off or some such thing.

Good luck!