Try un-installing all those packages through Windows add/remove programs. Then download and run these more recent installers.
matplotlib-0.98.3.win32-py2.4.exe
numpy-1.2.1-win32-superpack-python2.4.exe
wxPython2.8-win32-ansi-2.8.9.2-py24.exe
Make sure they all find Vizard's python installation. Do you still have the same problem?