Running xcas:
After unzipping xcas in a directory, click on
xcas.exe (english)
xcasfr.bat (french)
xcases.bat (spanish)
If you want to have print support you should install AsTeX, see
http://www.univ-orleans.fr/EXT/ASTEX
Once AsTeX installed, preview and print should work on windows NT. 
On windows 9x, you might need to edit the file
latex.bat with wordpad or notepad and remove the ^ before &latex2e

* Making a giac dll (Jean-Pierre Branchard)
make -f Makefile.win giac.dll
cp giac.dll /bin
ln -sf /bin/giac.dll /usr/local/lib
See also http://cygwin.com/cygwin-ug-net/dll.html#DLL-BUILD
Then you can compile giac applications using e.g. for Ginette
g++ ginette.cc -s -o ginette `gtk-config --cflags --libs` -lgiac