Hey Buddy its simple, even simpler then its in stupid Windows.
All you have to do is that you have to use Qt-designer with Kdevelop.
Wait a minute let me confirm that link....
just go to the website
http://www.kdevelop.org
In the website navigation bar at the left of the page there is a heading DOCUMENTATION and under that heading there is a sub heading TUTORIALS.
Click in front of tutorials, and it will show you the tutorials for Kdevelop and the first link for tutorial is
Qt Designer-3 and KDevelop-3
Just follow the link and you will learn it in maximum of 30 min.
Direct link for the tutorial is
http://women.kde.org/articles/tutorials/kdevelop3/
In this tutorial you just jum to the chapter3 which is
Creating the application
and follow the instuctions.
Wish you all the best.