The object model seems to be the same on old versus new Excel. If you record a VBA macro to unhide a workbook with this version of Excel you basically get:

 Windows("workbook_name.xls").Visible = True
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Which is what you get on earlier versions. Oddly, Visible does not appear to be a property of Windows in either version of Excel, so maybe it should have never worked. The way I was doing it was right out of Dave Roth's book. There's got to be a way with the current version of Excel to accomplish this!