Alot of my guild members who use our site have come to me complaining that the talent calculator seems to be tweaking out on them when they go to use. I went to see what the problem was and whenever you go to click on a talent in the calculator the 'Powered by Wowhead' opens up a big white box around it that flashes repeativly and makes it virtually impossible to click on the talent buttons. When your not scrolling over anything its a small little box in the upper left corner but the second you scroll over the talent's in the tree the box expands and is causing problems with the trying to check talents. Not sure if we are the only one who are experiencing this problem but wanted to let you know whats happening and hoping theres a simple solution to it since the Talent Calculator is pretty important in my guild at the moment and saves them time from having to search other sites for one.
So, it seems that their only options are to run Firefox, or upgrade to IE7.
Sorry I don't have a better answer, I don't know if they've ALWAYS had it broken like this for IE, I thought it used to work, but I could very well be mistaken.