Thanks Destructavator, did you get a chance to upload that new package yet? Gtkradiant is not compiling for me either. MinGW was updated using all the libs and binaries I could find from
http://www.gtk.org/download-windows.html and still
similar errors appear (except I found a much newer zlib library elsewhere.)
...\src\tools\radiant\plugins\entity\miscparticle.cpp:42: glib/gslist.h: No such file or directory
This looks like part of the glib library is just-plain missing. The gslist.h file can be found as part of the glib dev package at the above URL, however this didn't fix all the problems for me.
Also as an aside, if any newcomers were curious how to eliminate the "..mingw\include\jconfig.h:25: warning: "HAVE_STDLIB_H" redefined" error from the main project, simply remove the read-only attribute from .\mingw\include\jconfig.h and change the line that reads "#define HAVE_STDLIB_H" to:
#ifndef HAVE_STDLIB_H
# define HAVE_STDLIB_H
#endif
Then re-apply the read-only file attribute.