Thanks for the feedback on this! Having postponed my project, I'm just coming back to it now and only noticed these replies!
I took your advice Richard and bought the Sparkfun shield.
One problem is that the inverter they recommend doesn't seem to be available in the UK, where I am.
I have two inverters that I'd potentially like to be able to use. One is wrapped up with 4xAAA batteries in a pack - 'KD5' here - http://shop.surelight.com/EL_wire_inverters_2-10metres.htm
and the other is a standalone inverter which I currently am running from a mains outlet - 'L30' here http://shop.surelight.com/EL_wire_inverters_10-50metres.htm
With what I have (or indeed, an alternative inverter available in the UK!) would you guys be able to describe how I can set up the Escudo board to be able to power up to 20m EL wire? I am certainly no electrical engineer - so baby steps please!
Also, I have been reading the conversation at http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1269524229/all
but it seems to refer to a 5v inverter (and no one seems to have had much luck there either..)
Many thanks in advance