Please, help me! How can I mirror objects in blender?

1. Select object to mirror
2. Duplicate object by using SHIFT-'D' and then left clicking the mouse
3. press 'S' on the keyboard to scale
4. without moving the mouse press 'X', 'Y' or 'Z' for which axis you would like the object mirrored along
5. click the left mouse button to complete function.

Questions like this should be posted over at elysiun.com (the user forums) as the forums here are more directed at the programming side of blender.