Load data into input text form

I use this code to load data into my textarea:

jQuery('.content_container').load('http://www.evedalsvardshus.se/plugins/calendar/edit_dates.php', {'value': datum} );

But when I try to load data into my input text form with this code:

jQuery('.header').load('http://www.evedalsvardshus.se/plugins/calendar/get_header.php');

Nothing happens. The get_header.php contains only "asdsd".

Can anyone help me?