No need for freeware tools!
You can readily open the previous version's office file formats in latest versions.
So no problem at all!
In 2007You can open the .pst, .doc, .xls everything you created in 2003.
If you didn't purchased 2007, you can install Office 2007 compatibility pack.
After installing this with office 2003, you can access & create all office 2007 formats in office 2003 itself!http://www.microsoft.com/downloads/details.aspx?FamilyID=941b3470-3ae9-4aee-8f43-c6bb74cd1466&displaylang=en