Rendering problem

[mike.tzetz]

Hello,
I'm a new user to Blender and I have a problem on rendering. I use a macbook aluminium (late 2008) not pro, with 2 gb ram and NVIDIA GeForce 9400M 256 MB graphics and 2.4 ghz proccesor

The rendering result is like this;

http://imageshack.us/photo/my-images/16/45426411.jpg/

I've putted glass material on water with ior 1,333

On the other hand on pre-render, the render image is like this;

http://imageshack.us/photo/my-images/59 ... at103.png/