It's a common notion that latest is always better but in this case it was not so. People who had saved their office files in latest 2007 format found their files incompatible in computers running 2003 office applications. Thus, it put many a people under inconvenience. So it is better to use the 2003 office file formats till everyone is familiar with 2007. While saving, we may select 'save as' and then select 'type' as 2003 file format(ppt, doc etc) and click on OK. That will work but many of us are careless to remember doing that all the time, or worse still, many new users don't even know about selecting the type and all that stuff. So it's better to keep 2003 file format as default rather than the 2007 one.
I will show an example using MS Word 2007. I will change the format from docx to doc. The images below show step by step procedure.
Click on them to see full sized images.
I have given the example using MS Word application. The procedure is same for other MS Office applications too.
Also check, how to change colour scheme in Microsoft Office 2007 applications