mailchimp subscribe

Hi, I’ve set up a mailchimp RSS to email subscriber list (see thehappyeater.com.au)
However the form they provide in their widget is pretty ugly. I’d like to have a button the user presses that will open up another webpage with the mailchimp form to fill in (see Sarahwilson.com.au for an example of the subscribe button I’d like)
Can anyone give me a step-by-step on the plug ins and widgets I need to be able to do that?

Thanks for your help!
Sam