How to grab content of website automaticly?

I am bulding a website as news aggregator. When i add new url to my website i grab content of it and show users in a frame within my website. I need logic of news aggregator website which does all process automaticly. For example if i once add url example.com to my base it grabs automaticly content of latest post of that site and and grab its content.
Digg.com is a great example of it.