Table header focusable with keyboard

Hallo,

I`m using the table component. The table works fone for displaying and sorting. I need to implement that the table header elements are focusable by keyboard (using tabulator keys), not only by mouse.
What I want to do is the following: If the focus is set to the table (header), the first column header element is getting ths focus. Pressing Enter the sortable function is executed, using tabalutor key again, the next elemnt of header is getting the focus.

By the way I have to support IE 8, so I must use Vaadin 6.