How can I convert a vista word document to an office 2003 word document?

Install the Office 2007 Compatibility pack, it lets users (like me) who still only have Office 2003 to open and read and save files in 2007 format.

Download details: Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats

It is possible for some docs to "dumbed down" some during the opening in 2003, but that can't be avoided. There are some features in 2007 that have no equivalent or workaround in 2003.

But at least it works, I use it daily.