A nifty spell checker is available at the following link:
When installed, it will add a spell checker to the Internet Explorer tools. Also when you are typing in a message, you can right click your mouse button and select Check Spelling. You need to have your pointer outside the message editor frame, like on the Type in your message below: message just below the Attach a file link.
I have been using this for a week or so and have not found any bad effects from it so far.
You may also highlight an area (like you would for cutting and pasting) and just spell check that area if desired.