Javascript Vote Buttons, Check If User Has Already Voted?

I currently run a website similar to digg, where users can vote on a story. What I have been using so far to create the vote buttons, are just simply links that insert a vote into a database. And if a user tries to vote again on the same story, it attempts to insert the vote into the database, (im using MySQL btw), but when it cannot, they are redirected to a page where it tells them they have already voted on the story.

Now I thinking there has to be a better way to do this, and that's when digg came to mind. Can someone please point me in the direction of a javascript tutorial/wiki etc. on creating javascript buttons that interact with a mysql database AND remember that you have voted.