Why is my jquery tab based web site not working in IE7?

Why is my jquery tab based web site not working in IE7?

Hi,
I tried to build my first jquery web site and everything looks good in Safari, Firefox and Chrome. Only in Internet Explorer 7 on Windows Vista (I did not test IE8), it is a total mess. Unfortunately I am new to this and can not find the reason for it. Please help. :-)
Click the following link for accessing the  web site. Thank you very much.