hey, thanks for the answer.
It gave the push into the right direction.

Seemed to be more likely a java-problem, than a kindle one.

To cut everything short, I ended up with:

kta = new JTextArea(testString);
KPages _page = new KPages(_myPageProvider);
JScrollPane scrollPane = new JScrollPane(kta);

scrollPane.setPreferredSize(new Dimension(20,702));

_page.addItem(scrollPane);
_context.getRootContainer().add(_page);

that produced a text area over the whole screen, thats scrollable.

greets