Adding Widget area on the Header.php of Twenty Ten

the site just crashed

possibly just a php syntax eror – try again and double check the proper syntax.

without seeing what code you were working with, it is difficult to guess the cause.

also, don’t edit Twenty Ten directly, but create a child theme first to work with. http://codex.wordpress.org/Child_Themes
this will keep the modifications safe during an upgrade.

maybe have a look at http://wordpress.org/support/topic/adding-a-widget-under-the-banner?replies=15

details will depend on the exact location where you want the widget area to show in the header.