As I understand it, going from Zbrush directly into Second Life isn't possible without properly preparing your mesh for second life. The detailed models you'll produce with Zbrush will have millions and millions of polygons. You might make the most beautiful, life-like apple, but it would bring SL to a halt!
When bringing a model into second life, topology and mesh density (how many verticies) are really important considerations. If it's a subject that's still new to you, I reccomend reading up on it!
What I reccomend is to use Zbrush to create the fine details on your model, "bake" them into a texture map, and then upload a low-poly version of the mesh into SL that uses the texture you created through Zbrush. There are many steps in that process, and keeping it "simple" is difficult, because it is challenging.
Here is a tutorial I wrote about getting things from ZBrush to Second Life, but it's two years old now, and there might be better ways to do some of the things I mention in the tutorial.
Good luck! It is difficult, but worth the effort. I'm still learning about it.