I'm running two machines at the moment - one's running a recent build of Windows Vista RC1 and the other's running Windows XP. As you may know, the file format used by the upcomming version of Microsoft Office is different from that used in previous versions. If you find yourself needing to view documents from 2007 Office System on your existing Office System 2003 software then simply download (for free) a convertor - to save you hunting around for a convertor just click here. The convertor works well as it integrates directly with the existing Office installation such that you can open documents written in the new version just by double clicking on them as normal.
Simply double clicking on a document written in the new version results in a message pointing you to the convertor if you didn't already have it installed.