Download QT 4.4 sources for Windows on Trolltech website.

Unzip then and move the directory to C:\Qt.

Set the system PATH such that it contains C:\Qt\bin. It can be done by opening the Control Panel, then System, then go to Advanced and then Environment Variables. Make sure you do that before compilation. The Torch configuration procedure also needs it for finding QT.

Considering you have Microsoft Visual Studio, you can then do: 

cd c:\Qt
configure -release
nmake
Given the size of QT, allow few hours for compilation.