Installing Alfresco 4.2 on Debian 6 is not so hard. Just make sure you install the necessary libraries for LibreOffice and pdf2swf, otherwise the thumbnails and previews won't work properly.
We need the packages listed at http://docs.alfresco.com/4.2/topic/com.alfresco.enterprise.doc/concepts/install-lolibfiles.html but also a few others:
apt-get install libice6 libsm6 libxt6 libxrender1 libfontconfig1
apt-get install libgif4 libjpeg62 libpng12-0 libstdc++5 libxinerama1
After that, you can simply run the binary installer:
wget http://dl.alfresco.com/release/community/build-04480/alfresco-community-4.2.b-installer-linux-x64.bin
chmod +x alfresco-community-4.2.b-installer-linux-x64.bin
./alfresco-community-4.2.b-installer-linux-x64.bin
