Hi
I have imported an torso OBJ from Max to zbrush.
Poly count of obj in zbrush is 7042 low level
When div to level 4 is shows 1.786 mil
But in level 5 it becomes 7.144 mil which my system could not handle and starts to compact memory .
I need the Poly count which is around 2 or 3 mil to work the torso details.
I have 1gb ram and compact mem i have set to 760 and max poly per mesh 8
anyway i can get required poly count?
Every time you sub divide ANY mesh it will quadruple the poly count. 1 poly will become 4. and 1,000 polys will become 4,000, so on and so on. There is no way to change that or get around it without manually sub dividing only specific parts of the mesh and not the entire thing.
So for example, if your mesh in max is at 7,000 x 4 = 28,000 x 4 = 112,000 x 4 = 448,000 x 4 = 1,792,000 x 4 = 7,168,000 polys which is over your limit. 7,000 is a bad starting place for you. 
Basically what you need to do is some pre planing. Take the maximum poly limit that zb can handle for you, so like 3,000,000 and divide it be 4.
So 3,000,000 /4 = 750,000 /4 = 187,500 /4 = 46,875 /4 = 11,718 / 4 = 2,929
So that means you should either start with about 3,000 polys or a mesh that is closer to 12,000 polys in order to end up with about 3,000,000 polys.
Or just manually sub divide speicific areas of your mesh that need more detail and not the entire thing.
good luck 
Thanks for your reply
I will try to clean up the mesh in max to get low poly count.
My machine can’t cope with the weight of a fully subdivided whole figure: I always work on pieces of the character, splitting them off into sub-tools at natural, logical seams. You can do this after the event, (even after sculpting) by cloning the mesh in ZBrush and appending it to the original tool, deleting the bits you don’t want from each subtool.
Cheers,
R