I have one Excel file that is in 2003 format and needs to be saved in 2003 format. The problem I was having was when I saved the file as 2003 using Excel 2007, excel would always crash. This was happening on multiple computers with the file being stored locally. A side note was that if the file is saved as 2007, compatibility pack would also crash.
A fix that i found was to remove Windows Update KB908531. To do this go to Add/Remove Programs and check Show Updates. Scroll down until you fined KB908531 and delete it. Restart your computer.