trial/pay Qt SDK is only to develop (with Digia support) commercial progams.
For develop open source (and commercial) Qt are LGPL licensed:
http://qt-project.org/downloadsFor a more actual (2013-04-16) windows precompiled version (only uncompress and use):
http://sourceforge.net/projects/rallaz.u/files/librecad-win/librecad2.0.0beta1-git2013-04-16.7z/download