Since release 0.0.12 Mini-Commander is part of gnome-core. So if you are happy with it as it is there is no need for you to download and compile separate sources. Only if you are looking for the latest features or bugfixes this could be interesting for you. In this case you should first take a look at http://om.filewatcher.org/mini-commander/ to see if there is a new version at all.
Perhaps you also want to take a look at the history (Chapter 6) before or while downloading the sources.
The currently known latest separate sources package is http://om.filewatcher.org/mini-commander/mini-commander_applet-0.0.14.tar.gz.
But think twice before you download this package. The developement of GNOME is currently very fast. Probably this package will not even compile on your machine. Additionally Ryan Hayle reported that the Makefile is not being build correctly on his Debian 2.1 system. This might be the case for all Debian 2.1 systems. I have heard that you have to compile autoconf/automake from scratch to fix this problem. Perhaps it will be easier for you to get a package of the latest version of gnome-core which does already include mini-commander.