As requested we have now installed a built-in (cross browser) spell checker. I have tested it in Firefox and IE and it works well. It apparently also works on Mozilla/Netscape, Opera and Konqueror (Safari is unconfirmed).
To use just click on the ABC button...(Circled in red on image below). You will then get a window that pops up and checks your spelling and offers alternatives etc. the usual stuff.
Any problems, let me know.
Clancy
(Thanks goes to tamarian over at vbulletin.org for this excellent extension)