i don't know if it is the right way to make a universal app.

1) i have started with xcode a window app (very simple, only one button and a UIImageView).
it generates an iphone app (i can't choose universal with the wizard or i have not seen it).
2) changing it to universal it generates another xib ecc...

then i go to the window.xib and add buttons ecc...
when i run the app on iphone all is as expected, when i run on ipad, the button and other things are on the upper left.

there is a way to scale all and place buttons accordignly?
what is the best way to make an universal app?