Jan 28, 2006 update
: Google's new tool bar has a spell checker that works great with forum posts....
a spell checker that works with explorer. For all of us who type fast, are lousy spellers or just plain lazy, here is the program for you.
Go to http://www.iespell.com/
and download the program.
Its free (but donations are appreciated) and no ads or cookies.
It resides in your "tool" drop down menu in explorer. When you complete a post, before submitting it, click on "tools" and then "ieSpell".
Most convenient spell checker for the forums that I've found to date.