A “Sprog ii” is a DCC Decoder Programmer with a USB connector to your laptop. It is about the size of a matchbox and will fit inside the Hornby signal box.
Software for Linux is included on the CD which is supplied with the device. You install this software by unarchiving the file “JMRI.3.0-r20870.tgz” to any convenient location on your Home folder.
You then double click on the script marked “InstallTest”, which is in the JMRI folder.
If things don’t work, fire up the Ubuntu Software Center, and install “OpenJDK Java 7 Runtime”.