How do you create a twitter link that auto-populates the users status with some text?

How do you create a link (<a>) that will send the user to Twitter and auto-populate the sta开发者_开发知识库tus field with some text? I've clicked links like this before, but not sure how it's created.

Just as a note to anyone who finds this in 2014 onwards, Twitters API has moved on and you now have to use http://twitter.com/intent/tweet?text=

More info can be found on this blog article http://camgould.com/blog/posts/creating-a-link-that-posts-a-tweet

Point the link to http://twitter.com/home?status=some_text