You have to download/install it first:http://www.iespell.com/download.phpAs you can guess, it's IE only.
You can try the php spellchecker(pspell) for tinymce.http://wiki.moxiecode.com/index.php/TinyMCElugins/spellchecker
yes, like it is SO easy to get PHP on teamsite - just for the sake of spell checking...
Better - get a Mac and enable spell checking at the client level - then it doesn't matter what WYSIWYG editor you're using in TS - you have the Mac spell checking available to you ;-)