Learning blender

When I try to select a face on my model I accidentally select a face on the opposite site of the model, how do I disable this so I cannot see faces on the opposite site of the model?
Skorpio {l Wrote}:Click on the button that displays a cube in the header of the 3D view. It says: "occlude background geometry".
BTW do you use Blender 2.50? I still use 2.49 till a stable release is available. They changed the complete interface in the new version.