I am using a Netgear router again and can now connect to my Netra.
It's been a while:
Last login: Sat Dec 10 12:40:46 2011 from 192.168.0.3 Sun Microsystems Inc. SunOS 5.10 Generic January 2005 [scott@sparc ~]$
=)
The machine was given an IP address of 192.168.0.200 when I brought it home. My BT HomeHub seems to have had a range of 192.168.1.*, so it wasn't detecting the Netra when I made an ethernet connection.
I could have made a serial connection to the Netra, as advised, and changed its fixed IP - and I am going to learn to do that - but switching to the Netgear router 'fixed' the problem as by default it has a DHCP range of 192.168.0.2, up to .0.254 - so the Netra's fixed IP was visible, and I was able to ssh to it.
On the plus side, I now have a router I can actually configure - as opposed to the BT HomeHub which seems to be a locked down 'SpeedTouch' modem with no restore to factory settings feature or known login details (I tried the top google suggestions, no joy, so I was not able to change its DHCP range..)
Thanks.