OK I think I figured out what is happening. When I use the 4.5 installation, "make" is actually a batch file, C:\Qt\2009.01\qt\bin\make.bat, which internally calls mingw32-make, which is located in C:\MinGW\bin. For some reason, the 4.6 installation does not have this same batch file in C:\Qt\2009.05\qt\bin. Did something change between 4.5 and 4.6 as far as the preferred way to execute makefiles?