[jQuery] Need help with $.post()

The form that contains the data i want to $.post is dynamically
generated. So i do not know what elements it contains. Yet, i need to
post everything.
When i just use

$.post('file.php',function(){
  // Whatever
});

it sends no post-stuff at all. and i can *not* use:
$.post('file.php',{
  foo: 'bar'
},function(){
  // whatever
});