[Pierre_@_Spry]

The version of Debian installed on Spry's VPSes is stable. This OS is great, but the stability policy of Debian makes that some newer packages are not available for stable, while they are for testing.
Upgrading the distribution to testing is not recommended and could break your VPS.

The solution for keeping stable and installing the package is to modify apt-get configuration to setup what is called a mixed system:
-create or modify the /etc/apt/apt.conf file and make it contain the following line:

APT::Default-Release "stable";

-modify the /etc/apt/sources.list file: copy all the lines containing stable, insert them at the end of the file, and replace the stable in the lines you just added by testing. You must have all the original lines in the files plus all the lines where stable has been replaced by testing.
-run apt-get update to update the list of installable packages.
-if you want to install the package foo that is present in the testing sources, use the following command:

apt-get -t testing install foo

Be very careful about which packages you install from testing. By definition they are not as stable as the packages found in the stable distribution.