config.lua handling screen resolution

Hi all,
All my asset images are 480x320 pixels and I am using the following config.lua file to build my application

application =
{
content =
{
width = 320,
height = 480,
scale = “zoomStretch”
},
}

What is the difference between scale = “zoomStretch” and scale = “zoomEven”

Is this configuration file correct and can it handle the new iphone 4 resolution screen 960x640 pixels? Which scale value should I use?
[import]uid: 6661 topic_id: 3294 reply_id: 303294[/import]