Currently Wheezy (testing) and Sid (unstable) are supported.
Squeeze isn't supported any more because Sugar is in the progress of migrating to GTK 3 / Gnome 3, requiring bleeding edge versions of a couple of components.
In order to install sugar-jhbuild, you need to install git-core, lsb-release, python and subversion:
sudo aptitude install git-core lsb-release python subversion pkg-config
After installing and updating sugar-jhbuild according to the common instructions, you can use this invocation to install all dependencies automatically:
./sugar-jhbuild depscheck -s | sudo xargs aptitude -y install
Sugar will currently fail to start up because of Debian#648724. Until the package maintainer uploads the fix to the official Debian archive, you can build the patched package yourself. Sascha Silbe can provide binary packages for amd64, armel, i386 and maybe powerpc on request.
sudo apt-get install -t experimental gir1.2-evince-3.0 libevview3-3