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You have done everything right. The only thing you have left to do is to give "anonymous" users permission to see the block.
By default, when you make a custom block, the "webmaster" and "registered user" groups have permission to view the new block, the "anonymous user" group does not.
To set the permission, in the admin area, mouse over the system icon and click on "groups". "Modify" the anonymous group and check the box corresponding to the new custom block you made. This turns on the permissions.
Hope this helps. Stefan88 was right, just thought I would explain it in a little more detail if you found it confusing.
-Matt