install old version softwares with Macports

example: OpenCV 2.1

STEP1.
$ sudo port install subversion

STEP2.
check the location of the software in Macports trunk.

$port search opencv
Warning: port definitions are more than two weeks old, consider using selfupdate
opencv @2.2.0 (graphics, science)
Intel(R) Open Source Computer Vision Library

In this case, OpenCV located graphics/science/opencv

STEP3.
check a revision number of old version
http://trac.macports.org/browser/trunk/dports

STEP4.
download the old revision
svn co -r (revision number) (location of the revision)

$svn co -r 70430 http://svn.macports.org/repository/macports/trunk/dports/graphics/opencv

STEP5.
install the old software with MacPorts in the old revision folder.
$ cd opencv
$ sudo port install opencv

Ref:http://trac.macports.org/wiki/howto/InstallingOlderPort

日本語解説 (written in Japanese)
http://d.hatena.ne.jp/hoimei/20110303