For FF and other non-IE browsers, window.opener.outerWidth/Height give me the info I need. For IE, I'm still at a loss, from IE6 to 8. I can't use jquery as the opener's page is beyond my control, so I can't do a window.opener.$(window). This requires the opener to have jquery 'attached' (correct me if I'm wrong).
I googled quite a bit and also searched this site, still can't find a definite neat answer.
To add: I really need the outer size so that I can do a resizeTo(w, h) for the opened window where w and h are calculated based on a ratio of the opener's size. "resizeTo" ironically sets the outer size for IE and other browsers. I also tried a messy loads of stuff using resizeBy, not good enough.