Adding an Aweber email optin (or any email html capture form) is relativity easy on Facebook. It requires you to add an application to your Facebook Fan page or Facebook Business page.
1. Go to Facebook and search for the application FBML (Static FBML)
2. Add to page
3. Go to your page
4. Edit page – click the pencil and then edit
5. Get the form HTML code
6. Past into the fBML application
8. Choose FBML from boxes
Hope that Helps!