Two screenshots of what apparantly is a beta of Mac OS X 10.5 have been leaked, revealing what appears to be a desktop switcher and even Internet Explorer running natively in OS X.
http://www.picturetrace.com/images/leopard_img01.0.png
http://www.picturetrace.com/images/leopard_img02.png
http://www.picturetrace.com/images/leopard_img01.0.png
http://www.picturetrace.com/images/leopard_img02.png