Hello everyone!
I made this base mesh on Blender and imported on zbrush, but when i sculpt it affects the back faces too (the ones pointed by the red arrows)… is there an option to sculpt on the front faces only, without affecting the faces behind??
http://imageshack.us/photo/my-images/202/doubt.png/
Thanks 
Go to Brush > Auto Masking and turn on BackFaceMask
yes!!! thanks very much for that =)))
Also, it is preferable that you upload any images here and not link them externally.
ye, i tried it but it didnt worked… bot now i know how to do it, thanks again 
Your welcome and, yes, you prabably were just using the wrong image format the first time. JPG is probably the best and also you are allowed up to 500K size.