Yeah I have explained this in several threads. php has removed the pspell extension in php 5.3 and replaced it with something called enchant. SMF does not currently have any code that can use enchant. Internet explorer is the single remaining browser that does not have client side spell checking, so I don't know if anyone will bother using spell libraries server side anymore anyway. I suppose MS's dilemma is that they don't want to use their office spell checker without charging for it, and cannot use open source libraries without releasing any adaptations of it they make? Pure speculation. Either way I expect IE to have spell checking in the near future, they'd be fools not to add it. I expect due to corporate IE6 use someone will eventually make an add-on to SMF to use enchant that will eventually get merged into the SMF code, but it will not be me.
(I'm currently working on a css drop-line menu for the updated theme that will most likely not be IE6 compatible. Put Iron or FF portable on your flash drives folks.)
Or perhaps this is worth a try?:
http://www.iespell.com/I'm going to give it a whirl in IE8 on vista... will report. Oh 2006 looks kinda old...
Edit: I just spell checked this post with it in IE8 on vista - worked fine!