This forum will be replaced soon by newer version, I don't see any spellcheck feature or modification at the moment. The only one that was available for this version was through a third party that used a very obtrusive ad system if you wanted to use i so i never implemented it.
Anyhow there are other alternatives, I use the Google toolbar which has a built in spellchecker. If you don't want to install a toolbar, IEspell works very well which is an add-on for Internet Explorer: http://www.iespell.com/
If you're using another browser like FireFox there's other alternatives.