I finally managed to run RemoteWeb tests (PopupTest, DecoratedPopupTest and DialogBoxTest in -prod mode; on a Vista box with IE8 –which fortunately runs in compat mode and tests the user.agent=ie6 permutation–). It turned out there were a few bugs, and tests had to be updated (because I create the glass panel lazily when the PopupPanel is shown, instead of eagerly as soon as setGlassEnabled(true) is called)
http://gwt-code-reviews.appspot.com/113801 -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
