There is an updated version now that fixes many bugs, including
but not limited to the two most commonly reported ones (options
window had no close button, useless DOS window was shown).
Installation is done the same way as the previous package.

  http://csound.sourceforge.net/csound5gui.zip

> 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