The odds are that site was designed with MS Internet Explorer in mind, and not really tested with other browsers.
Each browser has its own Javascript interpreter built in, and they're not all quite the same, so there may be Javascript errors that show up when using one browser but which work fine on another.
Get the latest versions of Firefox and Opera, and try it with those. Firefox in particular has a really good Javascript debugger, so you can easily see what is causing the problem. If you still have trouble, even with those two browsers, try posting the error message(s) from the FF debugger; it'll give us a clearer idea of what the problem is.
Hope that helps