I have been using an application called ieSpell that I would recommend to those using Windows and Internet Explorer. It is an Internet Explorer plug-in that spells checks text input boxes by adding an option to the right click menu. It works very well for spell checking blog posts and comment boxes. It will work with any blogging software that uses text boxes on a web page, such as Blogger (all versions), Movable Type. P-Machine, etc. Here is their site and it is not spyware.
And while I am recommending software, here is another one that I use and would recommend. MyIE2 which is a browser that uses the core of Internet Explorer but has some added features like a tabbed window interface (like Mozilla and Opera), mouse gestures (like Opera), and many other features. Since it uses the core of IE the majority of websites which our optimized for IE will work flawlessly with this browser. Their site is here.