I don’t know if there is a spell checker associated with this site directly, but I have one for all my posts because I use Firefox as my browser. I believe Opera does the same thing.
Are you using IE?
If so, that’s why there is no spell check.
There is no built-in spell checker when you are writing a post. You should really give FireFox a shot. Whenever you misspell something in Firefox, it will put a red line under it like in Microsoft Word. Then all you have to do is right-click the word and see what spelling variations are available. Very handy.
I already corrected 3 spelling mistakes just from this post using FireFox :biglaugh