Ensure that a sources entry for Squeeze (Testing) exists in /etc/apt/sources.list:

deb-src http://http.us.debian.org/debian squeeze main contrib non-free

Run (as root):

apt-get update

Run (as root):

apt-get install fakeroot

Run (as root):

apt-get build-dep imagemagick

Change to a directory you'll be using for building.

For the next part you can be a regular user.

Run (which should automatically pick up the version from Testing)

apt-get source imagemagick

if not run

apt-get -t squeeze source imagemagick

This will download and unpack the latest source package. CD into the directory created that contains the unpacked source (imagemagick-6.6.0.4/ as of this writing)

cd imagemagick-*

Run

fakeroot debian/rules binary

and if all goes well, cd ..

In that directory will be a set of imagemagick debs that have only build-dependencies from Lenny (i.e. you just backported imagemagick for your environment).

As root again, run

dpkg -i *.deb