You can keep TB from cheking the spelling, simply uncheck 'check before send/queue' in the editor. This setting can found at the menu of editor under 'spell checker'. TB is supposed to remember this setting and does so over here.

As far as ignoring quoted text is concerned, I can't make TB check quoted text, it's ignoring it always. When you're quoting text, is each line of quotes preceeded with a '>'? That's the way the spell checker checks whether it's quoted or not.