I added the script line to our website (www.wasatchbroadband.com), and in Firefox it all works as I expected. In Safari on a Mac, however, neither the home page nor the Nites of Illyria page work right - there's no background on the tooltip. Yes, they're both in tables, but it does work on Firefox.
Safari doesn't dynamically load CSS properly. To work around this, add this line to your <head> section:
<link rel='stylesheet' href='http://i.thottbot.com/css/tooltip.css' type='text/css'>
Best regards,
Thott
P.S. I went ahead and added support for spells, so your Dreadsteed link will have a mouseover.