Get it here: http://windirstat.info/
[URL=http://img122.imageshack.us/img122/3338/20081225073918pq3.jpg][img:46a1f4d1fd]http://img122.imageshack.us/img122/3338/20081225073918pq3.th.jpg[/img:46a1f4d1fd][/URL]
more info: http://lifehacker.com/software/disk-space/geek-to-live--visualize-your-hard-drive-usage-219058.php
The only downside about it is that it rescans everything every time you start the program.  It doesn't save anything... so if it takes you 10 minutes for it to start the first time it will likely take 10 minutes to start every time.