Smooth Motion
The difference between 480i and 480p is in how frames are rendered. The "480" refers to the number of lines of pixels the screen can generate, while the "i" or "p" refers to "interlaced" or "progressive." An interlaced signal displays half of the current frame and half of the frame before it on alternating lines, moving too fast for the eye to make out the difference. A progressive signal displays only one frame at a time. This means the motion of a 480p image will be clearer and more "film-like," whereas motion at 480i has a hazy quality reminiscent of VHS recordings, where interlacing is standard.
Clear Images
Because a 480i image is made up of lines alternating between the current and previous frames, images are not displayed as clearly as they would be in 480p. This is particularly visible around edges and high-contrast areas, where very dark or light patches of the screen can take on a hazy quality. This is sometimes called "combing," or "mousetoothing" for the very fine jagged lines visible in the borders between light and dark. These lines also show up when a 480i display is rendering fast horizontal movement, as the current and previous frames are different enough that the eye can make out the interlacing.
Widescreen
A side-effect of upgrading to a cable capable of transmitting a 480p signal is the signal data being sent to the television is much higher. This means only a 480p-capable component cable will enable widescreen settings on the Wii. Once you have changed "Screen Resolution" to 480p in the "Screen" portion of the Wii menu, enter the "Widescreen Settings" portion of the menu. The option to display games in "Widescreen (16:9)" will now be available.