I don't know of any specifics, but this link may help, but I cannot access it due to work restrictions:
cari-mangsa.blogspot.com/2008/05/office-2003-service-pack-3-sp3.html
This is what the google description says about it:
"Some of the changes in Service Pack 3 modify the behavior of Office 2003, ... Certain macros in older Excel file formats have increased security"
I just tried a web search for "excel macros sp3 versus sp2"
Hope that helps.