As for the support for the Win32::GuiTest module, there are the following places when you can look for help:
perlguitest group at yahoo: http://groups.yahoo.com/group/perlguitest/join
Winguitest project on Source Forge: http://sourceforge.net/projects/winguitest
Currently, perlguitest is more active, so is you send your question there, you are more likely to get a response.
If you have some experience with perl, look at the module's documentation and the code. Look at provided examples and the test code. They are excellent in explaining how the whole thing works. If you also know C, try to get .xs file. You will see that many functions are actually simple wrappers for Win32 functions.
Understanding Win32 windowing mechanisms would be a big help. I can recommend you the following books:
Programming Windows 5th edition, by Charles Petzold - I can't say anything original here. Excellent book on Windows, a must read for someone who wants to get a grasp of what are Win32 all about.
Programming Applications for MS Windows 4th edition, by Jeffrey Richter - Another excellent book. Compared with Petzold, this book focuses more on system internals, whereas Petzold focuses on stuff related to windowing.
Programming Windows with MFC (2nd edition), by Jeff Prosise - Called "Petzold for MFC". Contains good explanation for toolbars and other controls.
Documentation for Win32 API can be found on Microsoft's MSDN.