I have a similar question.. I'm a little unclear with
your reply, so let me pose 2 scenarios.

Let's say I have 2 WBs, WB2003.xls was created with
Excel 2003, and WB2007.xls was created with Excel 2007.

Scenario 1: Can I bring up WB2003 and WB2007 at the same
time on the same computer, and have WB2003 appear as an
Excel 2003 WB while at the same time WB2007 appears as an
Excel 2007 WB?

Scenario 2: If Scenario 1 is not possible, can I bring up
WB2003 and have it appear as an Excel 2003 WB, then close it,
and then bring up WB2007 and have it appear as an Excel 2007 WB?