For assistance, click the link describing what you are doing:
Office 2007 Sending to Office 2003 Users
One Time Use Office 2007 - Saving as Office 2003
For Permanent Change of Format: Word: Make Word Save as 2003 Format (HowToGeek)
Excel: Make Excel Save as 2003 Format (HowToGeek)
Office 2003 Reading Office 2007 Files Office 2003 - Converting Office 2007 docs





