I can't remember when but I seem to recall a thread about adding a spell checker to this site. IIRC, the site isn't capable of adding that functionality.
However, I came across a nice work around. I added a Google tool bar to my browser and it has a spell checker that will check your spelling on any website you type on. It works pretty well too!
If you're a lousy speller like me you may want to give it a try.