There is a Win32 beta version now at this address:
  http://csound.sourceforge.net/csound5gui.zip
Currently, the stop button does not seem to work correctly when
not performing in a separate thread (this mode of operation is
only needed when using FLTK graphs and opcodes), and the "options"
window does not have a close button on Windows (you can still
close it with the Escape key, though). There may be other minor
bugs, these should hopefully be fixed soon.
To install the GUI, you need the 5.02 beta (single precision)
from SourceForge. Copy these files to the bin\ directory,
overwriting any already existing files with the same name:
  csound32.dll.5.1
  csound5gui.exe
  fltk.dll
this file should be copied to plugins\:
  widgets.dll

Not related to this topic, but the Win32 OSC plugin is also
available for those who are interested:
  http://csound.sourceforge.net/osc.tar.bz2