Start by looking through the many "polished metal text" tutorials you can find online. About 2 minutes of looking around netted one that seems not far from what you want to do: http://www.dreamdealer.nl/tutorials/pimp_your_text_with_photoshop.html I have no idea whether it's any good, but it can show you some ideas.
You can likely find some gemstones in a setting, and clone them into places as needed. Looks like they've transformed some to smaller sizes. Do the various parts in layers.
You can tweak your lighting effects, brightening some parts by hand so they seem to be making realistic reflections.
I'd probably also add a few flares to make the diamonds seem to be reflecting bright lights particularly brightly in a few places.
It's also possible that someone did up a 3D model and did a complete high quality ray tracing rendering.
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