The compilation of the Qt library fails because the compiler does not find the system header files (e.g. stdio.h or windows.h). Do you know what the problem is?

The problem is that you have not set the environment variables that are required to run the compiler on the command line. The Qt Installer has to run the compiler and this requires your environment variables to be set correctly. You need to set these variables to contain the paths of the compiler's header files and library files. Note that this is an option when installing Visual Studio. If you don't want to modify your global environment or don't know how to do this, then open a command prompt and run the vcvars32.bat/vsvars32.bat file that has been created by the Visual Studio installation, then start the Qt Installer from that command prompt. When using Visual Studio 2003 or 2005 you can use the command prompt provided with these versions, as this command promt will have the environment set up correctly.