I have made a png-image to the splash screen which is 320x480 so now i´m wondering how I´m going to do it. I have watched some YouTube tuts, but all are for earlier versions of Xcode that won´t work on my version, 4.3.
Oh my.. YOu should grab an book and learn about your IDE, on your Target on your project, there is a Summary, just drag and drop it on there >.<
And 320x480 is only 3GS, not Retina Support (which I suggest you should have also)
Xcode 4.3 doesn't exist, it's 4.2 max. When you click on Xcode on the upper left corner of your screen, and press, About Xcode, what version does it show?