Alternatively use a loop:
var oNewWin = window.open(....);
//Something to pass the time here.
Inside your loop you can do nothing, if the document can take a long time then you might want to look at using setTimeout to check for the new window.
I would have thought your code would have worked. Is the second page from the same server as the first? If not you will be forbidden access to the window and the DOM anyway by IE unless this is a "Trusted Site".
Joe (Microsoft MVP - XML