mono/mcs/class/System.Runtime.Serialization.Formatters.Soap

Build instruction:
extract the archive to the mcs/class/ dir

to build it on windows:
nant

to build it on linux:
make -f makefile.gnu install prefix=/pathtoyourmonoinstallationdir/

to run tests on windows:
nant test

to run tests on linux:
cd Test
make -f makefile.gnu test

If you want to use it with other applications, you have to reference it with "-r System.Runtime.Serialization.Formatters.Soap1.dll"