Boost setup for Debian lenny

Here is a description how you can set up the C++ boost library for a Debian lenny system. Sure, you could just use aptitude to install the lenny boost package. The trick is that you need sometimes (e.g. for the GENEVA library) the latest or a newer version then that, which is packed for lenny.
I will describe the method how i have done that and which i think is the most convenient one.
The first step: Add to the directory /etc/apt/apt.conf.d a file (in my case number 60 was "free") 60defaultdeb which should contain one line of config-code, which sets the debian default version, in my case stable "lenny" :

APT::Default-Release "stable";

The second step: Extend your /etc/apt/sources.list with the entries for the debian system you would like to use the boost library from. In my case, I am happy with debian testing (this one is called squeeze in December 2009) and the 2 additional lines in the sources list are:

deb squeeze main contrib non-free
deb-src squeeze main contrib non-free

The third step: You can (and should) make an apt-get update or being more up-to-date: aptitude update! Don't worry, nothing will change on your system just the squeeze/testing package lists are read.
The final step: Now you can install squeeze/testing packages by just using aptitude install packagename/testing or apt-get install packagename/testing, so for our boost use case:

aptitude install libboost-all-dev/testing

The advantage of using aptitude instead of apt-get is the nice feature that aptitude makes a detailed suggestion on howto solve potential dependencies and you can - if you are fine with that suggestions - just proceed the installation by accepting with "Y"!