During EclipseCon 2013 several people complained that Eclipse Forms is not available for pure Eclipse 4 RCP applicatoins.
I hope it helps to migrate existing applications that Eclipse Forms has been migrate out of any Eclipse 3.x dependencies. See Bug 369657 – FormsPlugin (Activator) unnecessary extends AbstractUIPlugin.
Please note that you should prefer CSS styling over the usage of Forms for new code. This Bugfix is supposed to help migrating existing code.