I made this in Photoshop and I plan to use it for my file sharing application:
I was wondering if it was possible to create GUI for my application that is gonna
Is not only possible but quite easy, you don't have to go all the way to create a custom Look and Feel.
This is what I've made in 20 minutes:
There is a lot of information on the web on how to customize the components without having to create a whole new L&F.
Understanding the Swing Architecture helps a lot.
Just in case you haven't read it the Swing Tutorial is here.
Finally you'll need the doc: Java doc