Well, you can do it like this, follow the tutorial:
https://www.youtube.com/watch?v=VwgDfVs8TNI
Or if you want to have another go at NGUI, try this tutorial, it has less audio, but a clear result:
https://www.youtube.com/watch?v=aMLANA6piVE
Try following those, and come back here if it didn't work out :)
You can also try out the Unity 4.6 Beta and use the new UI system there, Unity has their own youtube channel, and there are numerous High Quality Tutorials on the new UI System there :)
Best of luck! ^_^
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