I've once read somewhere that Windows can treat programs' executables and DLL files as parts of swap file rather than duplicating their content into pagefile.sys when swapping them out of physical memory. Is that true?
This is true.
For example: If you open notepad, then windows will load bits and pieces of the notepad.exe file from the hard drive. Then you write something in notepad. Then you minimize it and do something else that needs a lot of memory so that notepad gets paged out. The stuff you wrote will get page out to the pagefile, but the pieces of notepad.exe that were loaded just gets dropped, since they are already on the hard drive.
While this reduces page file usage, it does not increase your virtual memory. Windows still won't commit to giving more memory than RAM + pagefile.