trying to create a small project to reproduce the problem, I have seen that the problem of the text not antialiased is due to the lack of the HTML statament
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
When it is inserted all is ok also under IE 8, if not the problem is shown - please try to un/comment it in the page calling the RadWindow to verify the problem.
Unfortunately all my very enormous application has been developed deleting from any master page the doctype declaration otherwise I cannot use some effects of IE (namely the vertical positioning that is essential in my case).
Is there a workaround to get a correct behavior without the doctype declaration?
PS: It is not possible to send you a zipx file containing the test project from this forum, have you a mail where to send it?