I don't think you'll find something like "include this and everything will work magically", but you can have it ready in no time with a standard LAMP + jQuery implementation:
- UI: using regex you can easily validate e-mails. Google for that and you'll find tons of scripts.
- AJAX: jQuery AJAX methods are great, so I'd recommend that.
- With PHP is pretty easy to fetch your AJAX'd parameters and insert into the DB.
