now I get fatal error LNK1112, which tells my x64PC is not compatible with target type x86 Your problem is you installed the 64 bit Qt then you are trying to build Qwt in 32 bit mode. You can not link 32 bit code to 64 bit code or viseversa.
Make sure you have a 64 bit compiler if you want to build a 64 bit application. Visual Studio 2010 Express does not come with a 64 bit compiler. The following should help with that:
How to compile a 64-bit application using Visual C++ 2010 Express?
After you get a 64 bit compiler I believe you should run configure and nmake from a Visual Studio x64 command prompt to get the compiler to build 64 bit applications.
If you really do not need 64 bit applications a much easier approach is to install the 32 bit Qt SDK for Visual Studio 2010.
Here is the link for that: http://download.qt-project.org/official_releases/qt/5.1/5.1.1/qt-windows-opensource-5.1.1-msvc2010_opengl-x86-offline.exe
Remember that you can develop and execute 32 bit applications under 64 bit windows.