How to position SP.UI.ModalDialog

Hi

We're using SP.UI.ModalDialog alo on our project and have added the following fix to the css to make sure the dialog is always displayed within the visible part of the screen :

.ms-dlgContent
{
! important;

}

This has caused a further issue where we always get a blank rectangle on the screen when the dialog is shown in IE.  Does anyone know how to get around this?