Assuming you have installed Dev-Cpp in C:\Dev-Cpp
you should mention that path when installing qt-win-opensource-4.4.1-mingw.exe, when it asks for mingw.

After you install with the path of Dev-cpp, you should be able to run the qt apps with the console that is there in "Start->All Programs->Qt by Trolltech->Qt{version} command prompt"

But if you want to compile from cmd, and run apps with double clicks,
Just create environment variables as shown in Qt{version} command prompt
Assuming you know how to add env variables in windows, just
Add QTDIR & QMAKESEC to environment variables
and
append QTDIR/bin to PATH

restart the computer, everything should work fine.
You can ask if you want more detailed explanation. I might be slow in replying, though.