apt-get install package=version

gistfile1.txt

Before you install a specific version of a package you need it's complete version.
This will be displayed when you run:
apt-cache showpkg <package name>

e.g.
apt-cache showpkg subversion-tools

> Package: subversion-tools
> Versions: 
> 1.3.2-5~bpo1(/var/lib/dpkg/status)
> 1.1.4-2 (/var/lib/apt/lists/ftp.uk.debian.org_debian_dists_stable_main_binary-i386_Packages)

To install the specific version simply run run:
apt-get install <package name>=<version>

e.g.
apt-get install subversion-tools=1.3.2-5~bpo1