Showing 16:9 on MySpace Video Player
as detailed by Kisses from MySpace
Myspace player is only 4:3 320x240. To get 16:9 320x180 you need to add the black bars before uploading. So your 320x180 clip will have 30 pixel black bars on the top and bottom.

editors addition:
Formatting 16:9 in Premiere?
The Quick and Dirty Method is to render out your 16:9 project to an uncompressed AVI and then start a new 4:3 project and import your AVI into that, telling Premiere to maintain aspect ratio. This will allow you to maintain the image quality and resolution.