Steps for creating a "proper" Postgis 2.0 pacakge for Postgreql 9.1 on Debian Squeeze

I prefer to build in a chroot. Install debootstrap if you don't already have it. Change amd64 to i386 or whatever is necessary to suit your environment.

mkdir chroot
sudo debootstrap --arch=amd64 squeeze chroot http://ftp.debian.org/debian/

Prevent start-stop-daemon from starting daemons inside the chroot.

sudo bash -c "echo exit 0 > chroot/sbin/start-stop-daemon"

Bind mount the necessary directories from the host and chroot.

sudo mount --bind /proc chroot/proc
sudo mount --bind /sys chroot/sys
sudo mount --bind /dev chroot/dev
sudo mount --bind /dev/pts chroot/dev/pts
sudo cp /etc/mtab chroot/etc/
sudo chroot chroot /bin/bash

Since you are already root inside the chroot there's no need to use sudo going forward.

Configure locales in the chroot as things will break if this isn't done.

apt-get update
echo -e "en_US ISO-8859-1\nen_US.UTF-8 UTF-8" >> /etc/locale.gen
apt-get install locales

Add the official Debian backports repo and pin the postgresql 9.1 dependency packages. Also add debhelper, as version 9 is required for building GEOS, which is also available from backports.

cat >> /etc/apt/sources.list.d/backports.list <<EOF
deb http://backports.debian.org/debian-backports squeeze-backports main
EOF

cat >> /etc/apt/preferences.d/postgresql.pref <<EOF
Package: libpq5
Pin: release o=Debian Backports
Pin-Priority: 1000

Package: libpq-dev
Pin: release o=Debian Backports
Pin-Priority: 1000

Package: postgresql-client-common
Pin: release o=Debian Backports
Pin-Priority: 1000

Package: postgresql-common
Pin: release o=Debian Backports
Pin-Priority: 1000

Package: postgresql-server-dev-9.1
Pin: release o=Debian Backports
Pin-Priority: 1000

Package: debhelper
Pin: release o=Debian Backports
Pin-Priority: 1000
EOF

apt-get update

Install the dependencies required for building everything. The dependency tree here is rather large. Total download was 754 megs.

apt-get install build-essential debhelper postgresql-server-dev-9.1 doxygen swig ruby ruby1.8 ruby1.8-dev autotools-dev flex bison libproj-dev xsltproc docbook docbook-xsl default-jdk libpg-java fastjar libjts-java imagemagick libcunit1-dev dblatex libxml2-dev libgtk2.0-dev libgdal1-dev ant

Create a scratch directory to perform all the tasks and cd into it

mkdir scratch
cd scratch

Build a GEOS 3.3.3 package. I used the control files from wheezy.

wget http://ftp.us.debian.org/debian/pool/main/g/geos/geos_3.3.3.orig.tar.gz
tar xvf geos_3.3.3.orig.tar.gz
cd geos-3.3.3
wget http://ftp.us.debian.org/debian/pool/main/g/geos/geos_3.3.3-1.1.debian.tar.gz
tar xvf geos_3.3.3-1.1.debian.tar.gz
rm -f geos_3.3.3-1.1.debian.tar.gz
dpkg-buildpackage
cd ..

Install the newly created packages that are required for building Postgis 2.0.

dpkg -i libgeos-dev_3.3.3-1.1_amd64.deb libgeos-c1_3.3.3-1.1_amd64.deb libgeos-3.3.3_3.3.3-1.1_amd64.deb

Download the two patch files from this page into the scratch directory.

Build Postgis 2.0. This uses the postgis 1.5.3 control files from squeeze. The two patches are applied here to fix an issue with the Postgis itself (a bad URL in java/jdbc/build.xml to the maven jar that ant requires for building), and to make the control files build the package. Ensure that both postgis_debian-2.0.1.patch and postgis_maven.patch are in the scratch directory.

wget http://postgis.org/download/postgis-2.0.1.tar.gz
tar xvf postgis-2.0.1.tar.gz
cd postgis-2.0.1
patch -p0 < ../postgis_maven.patch
wget http://ftp.us.debian.org/debian/pool/main/p/postgis/postgis_1.5.3-2.debian.tar.gz
tar xvfz postgis_1.5.3-2.debian.tar.gz
rm -f postgis_1.5.3-2.debian.tar.gz
patch -p0 < ../postgis_debian-2.0.1.patch
rm -rf debian/source
dpkg-buildpackage
cd ..

Exit the chroot, umount the bind mounted directories from inside the chroot, copy the deb files that were created out, then delete the chroot.

exit
sudo umount chroot/proc
sudo umount chroot/sys
sudo umount chroot/dev/pts
sudo umount chroot/dev
cp chroot/scratch/*.deb .
sudo rm -rf chroot

You'll have to add the backports repo and pin the Postgres 9.1 packages to the "host" distro before installing the packages:

sudo bash -c "cat >> /etc/apt/sources.list.d/backports.list <<EOF
deb http://backports.debian.org/debian-backports squeeze-backports main
EOF
"

sudo bash -c "cat >> /etc/apt/preferences.d/postgresql.pref <<EOF
Package: libpq5
Pin: release o=Debian Backports
Pin-Priority: 1000

Package: libpq-dev
Pin: release o=Debian Backports
Pin-Priority: 1000

Package: postgresql-9.1
Pin: release o=Debian Backports
Pin-Priority: 1000

Package: postgresql-client-9.1
Pin: release o=Debian Backports
Pin-Priority: 1000

Package: postgresql-client-common
Pin: release o=Debian Backports
Pin-Priority: 1000

Package: postgresql-common
Pin: release o=Debian Backports
Pin-Priority: 1000

Package: postgresql-contrib
Pin: release o=Debian Backports
Pin-Priority: 1000

Package: postgresql-contrib-9.1
Pin: release o=Debian Backports
Pin-Priority: 1000

Package: postgresql-plperl-9.1
Pin: release o=Debian Backports
Pin-Priority: 1000

Package: postgresql-server-dev-9.1
Pin: release o=Debian Backports
Pin-Priority: 1000
EOF
"

sudo apt-get update

Install the pacakges. This command line would install all packages created by this process. Obviously don't pick anything you don't really need. For example, I have no use for the GEOS ruby bindings or the Postgis java package.

sudo dpkg -i libgeos-3.3.3_3.3.3-1.1_amd64.deb libgeos-dbg_3.3.3-1.1_amd64.deb libgeos++-dev_3.3.3-1.1_amd64.deb libgeos-ruby1.8_3.3.3-1.1_amd64.deb libgeos-c1_3.3.3-1.1_amd64.deb libgeos-dev_3.3.3-1.1_amd64.deb libgeos-doc_3.3.3-1.1_all.deb libpostgis-java_2.0.1_all.deb postgis_2.0.1_amd64.deb postgresql-9.1-postgis_2.0.1_amd64.deb

Pull in the new deps.

sudo apt-get -f install