Download
CVS: You need to type the following commands to get it:cvs -d:pserver:anonymous@cvs.sourceforge.net:/cvsroot/insomnia login
when prompted for a password simply press enter
then type the following:
cvs -z3 -d:pserver:anonymous@cvs.insomnia.sourceforge.net:/cvsroot/insomnia co fall
That's the first time, the next time you should move to the directory where the code is and simply write cvs -z3 update
If you don't know what is CVS you should look at the Tools section of the main page.
Tar ball
The source code can also be downloaded here
Win32 binaries thanks to Sphair are here