I have finally figured out how to get the ERLE Robotics image below working on my BBB:
https://mega.co.nz/#!6EcDRTZI!y-msWeHYUsTtWdLTYcq8XNIs2BWlpc8sFK5SiOB5Zlg

Thanks to Patrick at the ERLE forums for advising that this image disables the HDMI output and the Ethernet output (it does this to free up more CPU cycles to run the ArduPilot and other software).  This is why I wasn't seeing either.  It does however have a network connection via the miniUSB port (the same one you can power the BBB with).  I am running XUbuntu on my laptop and when I plugged the BBB into my laptop via USB (I was using a USB power brick previously which is why I didn't see it) it immediately brought up a new ethernet device eth1.  It was then a simple matter of running

sudo ifconfig eth1 192.168.7.1
ssh root@192.168.7.2

and I was logged into my BBB.  Note that there is no password for the root user.  There is also a debian user created but I couldn't guess what the password was for that so I just used root.

Why did I go to all this trouble rather then use the standard Debian image - so I didn't have to recomplie the kernel to get the Real-Time functionality.  This image comes with it by default.  It also has a release of ArduCopter.elf installed and running by default.  I know we want to run Rover on it but it means all dependent libraries are installed correctly so when I copy my APMrover2.elf across it should just work.

If you want the Ethernet interface to work you need to edit (use nano if your unsure) the file
"/etc/network/interfaces" and uncomment the following 2 lines.
auto eth0
iface eth0 inet dhcp

I have found a little patience helps.  Sometimes it takes a minute or two for it to bring up either the ethernet or usb eth1 network interfaces after boot.

Now to plug in a PXF board and see what happens :-)

Love to hear from everyone on their progress.

Thanks, Grant.