You will need: Pidgin source code distributable, Pidgin Win32 distributable, and an "all-in-one bundle" of the GTK+ stack 2.14.7 or greater (e.g., gtk+-bundle_2.24.10-20120208_win32.zip from http://www.gtk.org/download/win32.php).
In Makefile.mingw, specify the location of PIDGIN_HEADERS, PURPLE_HEADERS, GTK_WIN32_BUNDLE, and PIDGIN_WIN32_LIBS
Ensure either pkg-config will correctly resolve all the dependencies for glib-2.0 and gtk+-2.0 (there is a README in the GTK+ bundle about this), or uncomment (and perhaps revise) the hardcoded list of includes for GTK_HDRS
make -f Makefile.mingw
nsis:
sudo apt-get install nsis
Locate the "nsisunz" plugin (a google search for "nsisunz.zip" should be sufficient)
Extract the DLL to /usr/share/nsis/Plugins (yes it's a DLL extension, but it will still work for GNU/Linux nsis)
set LIBOTRSRCDIR to the libotr src directory
make -f Makefile.mingw installer <-- This should now build the nsis installer
make -f Makefile.mingw zip <-- This should now build the zipfile
# Locate the "nsisunz" plugin (a google search for "nsisunz.zip" should be sufficient)
# Extract the DLL to /usr/share/nsis/Plugins
# (yes it's a DLL extension, but it will still work for GNU/Linux nsis)