You should have a little bit of experience with Linux for this to be easy.
Install MPlayer with MEncoder with XviD and DVD support. If your distribution does not have a package for this then you will have to build it yourself. Refer to the MPlayer documentation for instructions on how to do that.
Install a Java runtime environment 1.4 or higher. Check to see if your distribution has packages for this.
Install SWT. Use your distribution's utilities if possible.
Open a terminal and run
$ tar -xvjf iriverter-VER.tar.bz2 $ cd iriverter-VER $ ./configure --with-swt=/path/to/swt.jar $ make # make install
Start iriverter by clicking the menu item in your Sound & Video menu or by running iriverter on the command line.
If you'd rather use GCJ than Java to build iriverter, append --with-gcj
to your configure command. The rest of the instructions are the same.