WordPress MU

Hi to all,
Is there any way to category the blogs. Some thing link science, studies, funny and games some thing link this. If we see science under that we can able to see 10 to 20 blogs related to science. some way for funny, studies and games also.
See this..
Science
  |_One
  |_Two
  |_Three
  :
  :
  |_Ten
It is same like category the blog posts. once we category the blog post. If we click on that category we can see more post, which are categorized under that.

Try this plugin.

http://wordpress.org/extend/plugins/blog-topics/

(I just updated the readme, because apparently when I last updated the code the readme file didn't update. So, if the info on the site doesn't match the downloaded readme, it's because the site hasn't updated yet. The download should be correct.