Doh!
Kabooom! Ian's great idea crashes and burns
How do I find out what version I have installed on my R Pi ?
Oh, it says so right there in the boot up script, it says:
Debian GNU/Linux 7.0 raspberrypi tty1
and then a little further down it says:
Linux raspberrypi 3.2.27+ #250 PREEMPT Thu Oct 18 19:03:02 BST 2012 armv61
So I hadn't actually gotten to the point of writing anything in C#, copying it across to the Pi and then trying to Mono Run it.
Oh well.... Python it is then