[SOLVED] How to use Ui forms as a simple Dialog?

[tofighi]

In the Qt Creator I have two options to add a form:
New->Qt-> Qt Designer Form Class
New->Qt-> Qt Designer Form

I want to use Qt Designer to design an "About this software" Dialog and run it from MainWindow menu. I know how to do this via Qt Designer Form Class, but I think it doesn't need to add about.ui, about.h and about.cpp to my application for doing this.
I believe it should be possible to do such an easy job only by using

New->Qt-> Qt Designer Form

but I don't know how use ui form itself as a Dialog. Please give me some directions.