Howdy,
The build instructions for Win32 developers (http://inkscape.org/win32/win32buildnotes.html) point to a zip file with a self-contained Mingw installation:

<blockquote>
Note: Temporarily, I suggest that people use the preassembled Mingw working directory that we have assembled here. It has the important pieces set up to compile the way we need them. Unzip it to c:\mingw.
</blockquote>

This is great, except that the installation is missing some files. When I tried to build Inkscape on a fresh copy of Windows XP with this package, I encountered several build errors. To solve the problem, I unpacked the following official Mingw packages on top of the broken Inkscape-provided installation:

gcc-core-3.4.2-20040916-1.tar.gz
gcc-g++-3.4.2-20040916-1.tar.gz
mingw-runtime-3.9.tar.gz
w32api-3.5.tar.gz

This fixed the issues. Now that my Mingw install works, I've packed it up into an archive and placed it at www.swansontec.com/temp/mingw.7z . It would be great if someone with access to the server could replace the existing Mingw package with this one. The current URL is just my temporary file-transfer space, so the file needs to move to a more permananet home before linking to it.

-s_tec