Thanks Marcus
I decided in the end that installing mono for a single WebService (which was only ever a proof of concept) was probably overkill - so now I'm using PHP to talk to MySQL.
So, in the space of 36 hours (elapsed), I've ported over 2 websites and a mail server to the Plug using Apache, MySQL, PHP and Postfix - and there's still room to spare without adding any cards - so I'm well chuffed
