The Bcfg2 source tarball can be grabbed from the Download page.
All tarballs are signed with GPG keys 7F7D197E or A88FFF4B. You can verify your download by importing the keys and running
gpg --recv-keys 0x75bf2c177f7d197e 0x80B8492FA88FFF4B
gpg --verify bcfg2-<version>.tar.gz.gpg bcfg2-<version>.tar.gz
You can also get the latest (possibly broken) code via git
git clone git://git.mcs.anl.gov/bcfg2.git
If you are working with the release tarball of Bcfg2 you need to untar it before you can go on with the installation
tar -xzf bcfg2-<version>.tar.gz
Now you can build Bcfg2 with. If you are working from a git clone no <version> need to be specified.
cd bcfg2-<version>
python setup.py install --prefix=/install/prefix
This will install both the client and server on that machine.