Installing from ORBit2 source code is very easy. You need to have glib version 2.0.0 or later series installed. To see if you have glib installed (and what version) go glib-config --version
You can obtain the latest version of glib from http://www.gtk.org/
Now just download the latest stable tar ball of ORBit. Start by going to the gnome web site (http://www.gnome.org/), choose download and find your closest mirror site.
ORBit installs as a standard gnu application, so going ./configure followed by make and then getting root permissions and make install will do everything as expected.
What to do if you don't have root permissions Basically you want to run all of the above but with ./configure --prefix=<installation location> which will install under prefix/bin /libs etc.
If ORBit2 2.7 does not compile with some commercial C compilers, this is because it uses a number of gcc extensions which are not supported elsewhere. you can always download gcc and install that for it to work.