The install section mentions running perl makefile.pl but the archive mentioned (http://www.sourceforge.net/projects/winguitest) doesn't include that. There's makedist.pl, but that can't find some files and seems to be trying to build the archive it came out of...
The .ppd file included with the archive won't install, mainly due to the line:
<ARCHITECTURE NAME="MSWin32-x86-multi-thread-5.8" />
Changing that from 5.8 to 5.14 lets it install but then perl.exe throws an unhandled exception as soon as use Win32::GuiTest appears in my test script.
The archive from cpan (http://search.cpan.org/CPAN/authors/id/K/KA/KARASIK/Win32-GuiTest-1.59.tar.gz) does have a nice makefile.pl, but gives the same result that cpan install Win32::GuiTest did.