There is no change in PerformancePoint functionality in using Excel 2003 or Excel 2007. Obviously users of Excel 2003 will not be able to take advantage of the great new business intelligence features in Excel 2007 or the PPS specific ribbon that we have built. But as far as PPS goes, the server based functionality is the same.
Also, there are “light-ups” in planning forms that you won’t get in 2003. Basically, it’s formatting options. The pivot styles that we leverage to do dynamic formatting only come in 2007 so you’ll get better options and preservation of visual display in forms on 2007 than 2003