Getting svn
To get the current development snapshot, you will need svn. On linux this is usually present, as the command svn.
On Windows you can use TortoiseSVN:
http://tortoisesvn.tigris.org/
On Mac use scplugin for Finder:
On OSX refer to this page:
http://www.wikihow.com/Install-Subversion-on-Mac-OS-X
Other platforms are listed here:
http://subversion.tigris.org/project_packages.html
Getting the development code
The command to check out the repository from the linux command line is:
svn co http://modular.math.jmu.edu/svn/mpir/
If you wish to commit to the repository, you will need an account --- please ask on mpir-devel.
Using svn
The basic svn commands are described here:
http://www.linuxfromscratch.org/blfs/edguide/chapter03.html
You can also revert files in your local copy to the last version you checked out by using:
svn revert filenames