Hiya.
Absolutely, but AFAIK once you've started sculpting details you can't go back to the ZSpheres.
Though I wouldn't really care if I'm wrong, since Sculptris is free
Jibb
Just a note here.
In ZBrush 3.5 (latest version) you can build your 'armeture' of ZSpheres, then go into what is called "ZSketch". You can go back in and add/subtract/move/etc your ZSpheres all you want. You can do this either with your 'ZSketch' work bound to it or not (if bound, it moves 'like muscles' in a way, when you move the ZSpheres).
Anyway, go here:
http://www.pixologic.com/home.php For the latest ZBrush info...and spend some time browsing around the place. Lots of amazing stuff to be seen here (hit the forums for sure!)
As for this little tool...looks pretty sweet from my view. I can see a LOT of people (re: modelers) really cranking out some nice normal maps now! And 'proper' normal maps too...not ones auto-generated from a 2D pic with some plugin. Looking forward to seeing what people come up with.
(PS: I still HIGHLY recommend ZBrush simply for all the other amazing things you can do with it in a production envrironment...not to mention the company, Pixologic, totally ROX ON TOAST!)