Some stations broadcast DH in 720p and some in 1080i. The 480i you are receiving is a standard def picture, but if it is digital, it will be a better picture than if you were picking up analog stations of the same material.
Got a new Samsung 4665F delivered today. Not hookig up hidef until Wed. I am currently picking up some digital channels over the air. Some are shown as 420i, some as 720 and some as 1080i. Is 480i standard braodcast?