I sent this to you via PM, but I figured others might want the information, too:
You can get the Nox spell server from
http://orangoo.com/labs/GoogieSpell/Download/Nox%20Spell%20Server/ and there are instructions there on how to install it. Once it is up and running, find this section in the RoundCube main.inc.php file, and set the variable like so:
// For a locally installed Nox Spell Server, please specify the URI to call it.
// Get Nox Spell Server from [url]http://orangoo.com/labs/?page_id=72[/url]
// Leave empty to use the Google spell checking service, what means
// that the message content will be sent to Google in order to check spelling
$rcmail_config['spellcheck_uri'] = '127.0.0.1:14003/?lang=';
That should do it. Sometime after Christmas I'll write some (better) instructions for this and put it on the Wiki.