Taken straight from here
"In iOS 3.2 and later, an iPad application can provide different launch images depending on whether the device is in a portrait or landscape configuration. To specify a launch image for a different orientation, you must add a special modifier string to the base file name of your standard launch image. Thus, the format of each file name becomes the following:
[basename][orientation_modifier][scale_modifier][device_modifier].png
"
So in your example you could have:
Default-Landscape.png
Default-Portrait.png
(Default-Landscape@2x.png for iphone 4 and Default-Landscape~ipad.png for ipad and so forth...)
both have to be 320x480 and you'll have to ensure that your app's Info.plist
contains all 4 UISupportedOrientation
values (UIOrientationPortrait, UIOrientationLandscapeLeft etc etc). But see my above link for a better explanation.