I implmented SpelChek on my forum without an issue (vB 3.0.1). I followed all the steps without issue. The only modification I did was to use class="button" in place of the style stuff (font color, etc) that is provided in Code Snippet #2. Also, the HTML page that you create to generate the two code snippets doesn't work under Opera 7.5b1.
I just did this so it's fresh in my mind - if anyone has any questions after trying it, please let me know.