In mootools I would do something like $(\'form_id\').send({success:function(res){....}});
What is the parallel syntax in jQuery?
Another words:
How
There is nothing that ships with jQuery that will automatically AJAXify a normal form for you.
Option 1 -- Intercept the form's submit event, scrape the data from form fields using serialize, and send using ajax or post, as suggested.
Option 2 -- Use this great forms plugin, which does all of option 1 for you.