How to use QT GUI DLL from another application?

[online.0227]

Hello~
please note that I am not a native in English. sorry for any grammar mistake.

I am very new to QT(just started yesterday) and have only few experiences with MFC. I want to know how to integrate QT GUI DLL into non QT application.

I made this QT GUI DLL from the wizard: I simply chosen QT Gui Application and in .pro I changed "TEMPLATE = app" to "TEMPLATE = lib", as well as changing source code.

I attached source code here, you may looks at it.
http://cfile208.uf.daum.net/attach/025A524151C3E65D1B5E63

in the zip file, sources in folder "gui" does creating GUI DLL. sources in folder "main" actually loads DLL and try to call the function in DLL.

they compiles well, but it seems they do not work. it gets an error called "there should be only one application object" when I start main.exe

What is the problem?