Polishing aluminum will temporarily make it shiny. As the metal is still bare, it will eventually go chalky and gray again as oxidization occurs.
Sand blasting or bead blasting will clean it in preparation for proper finishing. If you just leave it like that, it will once again just oxidize.
Unless an aluminum frame is anodized, painted, or powder-coated, it will always oxidize and end up looking like crap. Anodizing a single piece was kind of expensive, last time I checked. Painting can produce the best custom result, but can be expensive too. Powder-coating is relatively cheap and very durable. I've seen silver powder-coated aluminum frames that you'd swear were just polished or clear-anodized. It's the way I'd go. Just make sure the BB shell threads and inside of the seattube at the collar are masked off so they don't end up with a layer of powdercoat on them.
Last edited by Torchy McFlux; 07-09-10 at 04:20 PM.