Determining the maintainer is easy :)

• You can report a module issue at CPAN RT. The author will automatically get mail about it. If you encounter a porblem, that's where you should report it (although chekc the docs for other preferences). Very few CPAN authors read Perlmonks looking for bug reports.
• Look at CPAN Search for that module (Win32::GuiTest). CPAN Search collects a lot of module meta data in one place. You'll find lots of interesting stuff.
• Read the module documentation (perhaps using perldoc). The maintainers are usually listed at the end of the docs.
• If you have a PAUSE account (although most Perl users don't), there is a "View Permissions" tool that can search by author or module
• The cpan tool that comes with CPAN.pm (which comes with Perl) has a -D switch to show module details. Note that the module names are case sensitive:

   
  $ cpan -D Win32::GuiTest
  Win32::GuiTest
  --------------------------------------------------------------
          SendKeys, FindWindowLike and more
          K/KA/KARASIK/Win32-GuiTest-1.54.tar.gz
          Installed: 
          CPAN:      1.54  Not up to date
          Dmitry Karasik (KARASIK)
          dmitry@karasik.eu.org
  [download]

Good luck :)