IE6sp2 will not be able to handle the site and yes will cause a crash. IE6sp3 and IE7 can. The latest version of Opera has no problems as well handling the site. As for AJAX, here is the wikipedia link to describe it better than I would be able to.
Interesting. This is the first website I have encountered that IE6SP2 failed to load. So is it some of the AJAX programming that would cause this?