hm...guys, how to play a real full screen video at iphone 3g ar?

i try to upload some videos to my iphone3g, when i play the video using my iphone, the up and down part of the video is black
when i double tap the screen, it will zoom in and play in full screen, but then it is zooming in, meaning the right and the left side of the video is missing and i cant see it

any idea how to play it in real full screen, where the side part wont be missing? or use what application to play it other then ipod?
PS: hope you guys understand what i mean

hm...ok, i download the original video from the net, which is in .mov format
then i use itunes to convert it to a format where the iphone can play
PS: the orignial movie also got black part in the top and down if i play in my PC, but since i using windows media classic to play it, i can pan and scan to make it become real full screen

so i was asking is there any function like this for iphone?
coz last time i use HTC TYTN2, when i double tap, it will automatically become real full screen