Checking if your kit is complete...
Looks good
Writing Makefile for Win32::API::Callback
Writing Makefile for Win32::API
cp API.pm blib/lib/Win32/API.pm
cp Struct.pm blib/lib/Win32/API/Struct.pm
cp Type.pm blib/lib/Win32/API/Type.pm
cp Callback.pm blib/lib/Win32/API/Callback.pm
cp Test.pm blib/lib/Win32/API/Test.pm
make[1]: Entering directory `/export/home/cpanrun/depot/main/contrib-patched/perl/CPAN/src/Win32-API/Callback'
/export/home/cpanrun/build/5.6.1/bin/perl -I/export/home/cpanrun/build/5.6.1/lib/5.6.1/sun4-solaris-thread-multi -I/export/home/cpanrun/build/5.6.1/lib/5.6.1 /export/home/cpanrun/build/5.6.1/lib/5.6.1/ExtUtils/xsubpp  -typemap /export/home/cpanrun/build/5.6.1/lib/5.6.1/ExtUtils/typemap Callback.xs > Callback.xsc && mv Callback.xsc Callback.c
gcc -c  -DUSE_REENTRANT_API -D_POSIX_PTHREAD_SEMANTICS -D_REENTRANT -fno-strict-aliasing -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -O   -DVERSION=\"0.47\" -DXS_VERSION=\"0.47\" -fPIC -I/export/home/cpanrun/build/5.6.1/lib/5.6.1/sun4-solaris-thread-multi/CORE  Callback.c
Callback.xs:17: windows.h: No such file or directory
make[1]: *** [Callback.o] Error 1
make[1]: Leaving directory `/export/home/cpanrun/depot/main/contrib-patched/perl/CPAN/src/Win32-API/Callback'
make: *** [subdirs] Error 2