I've debugged the page a bit, and found the following:
1.) The problem only affects versions 5 and 6 of IE, in IE 7 everything works fine
2.) The file that lets IE 5 and 6 crash is "shapeimage_7.png". Go to your iDisk, navigate to the "Web" folder, to your site, to the Welcome_files folder and remove the file shapeimage_7.png. IE 5 and 6 won't crash anymore. Maybe you can find out for which graphic iWeb uses that file and modify that element in iWeb so that you won't have to manually delete the file after every update of your site.
In any case, this is a bad bug in IE that might be used to hack a computer, too. I guess you should notify Microsoft. Even though the bug doesn't affect IE 7 in this case, it could still be used to hack that version, too.