creating Sign-up form on Facebook
You can get an HTML snippet for a Profile and include as an iframe. This option should show under 'more' to the right of the profile listings.


  HTML Form Snippet - If you want more control over form layout, or want to add Profile input forms to non-CiviCRM blocks, pages and/or sites...click the HTML Form Snippet action link for a Profile below - and copy and paste the HTML form code into any web page.


NOTE: there is now a setting in Administer => System Settings => Misc to enable this.