Debian packages for CGAL 4.1 are now available as well. Simply add

  deb ftp://ftp.mpi-sb.mpg.de/pub/outgoing/CGAL/debian squeeze main
  deb-src ftp://ftp.mpi-sb.mpg.de/pub/outgoing/CGAL/debian squeeze main

  deb ftp://ftp.mpi-sb.mpg.de/pub/outgoing/CGAL/debian wheezy main
  deb-src ftp://ftp.mpi-sb.mpg.de/pub/outgoing/CGAL/debian wheezy main

to /etc/apt/sources list (you only need the pair of lines corresponding
to the release you are using). For sid, packages should be available
from the official Debian repository in a few days. The packages are called
libcgal10, libcgal-dev, libcgal-qt4-10. libcgal-qt4-dev, libcgal-demo, and
libcgal-ipelets.

In case you want to download the packages manually, have a look at
ftp://ftp.mpi-sb.mpg.de/pub/outgoing/CGAL/debian/pool/main/c/cgal/

See also https://www.cgal.org/FAQ.html#debian_packages .