I was writing some code in Qt Creator (on WinXP) last night, and I'm not sure what I've changed, but for some reason it started having problems compiling, saying things like:

Qt Code: 
  1. Could not find make command: mingw32-make.exe in the build environment
  2. Error while building project blockingfortuneclient (target: Desktop)
  3. When executing build step 'Make'
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and in the options menu it says:

Qt Code: 
  1. Qt in PATH <not found>
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I don't have much experience with this, but from what I've figured out, I need to add the Qt directories to 'PATH' in the Windows XP System Properties -> Environmental Values tab, but I don't understand why.

Even though the problem is basically solved, I still have a few questions about the whole 'PATH' thing.:
  • Why can't Qt (and other similar software development applications) locate it's own directory and compilation executables? Surely it knows where it is installed to, right?
  • Exactly which directories do I need to add? Can it just be the 'C:\Qt\2010.05\' directory, and then Qt can navigate to sub directories, or do I need to go all the way to the required executables (e.g. 'qmake.exe' being in the 'C:\Qt\2010.05\qt\bin\' folder)?
  • What is the difference between 'PATH' in the 'user variables' section, and 'Path' in the 'system variables' section?