Stupid problem with the mirror modifer (2.46 RC1)

My problem with the mirror modifer is really simple: It doesn’t work!
Is it broken? Iam using Blender 2.46 RC1 with a simple default scene with the default cube.
After adding the modifer nothing happens.

To grant that this is not caused by an option or scene, i tested it with the default scene.
Does anyone else got problems with it?

EDIT: This can be closed, iam so stupid as the title mentioned.....Because the mirror was on the same spot as the originial object.