vista --- offcie 2007

You may install Office2007 on your existing WinXP not only to Vista.
If you are currently using XP office or Office2003, you will need to install the Microsoft Office Compatibility Pack which you can be downloaded at Microsoft site below:

http://www.microsoft.com/downloads/details.aspx?FamilyId=941B3470-3AE9-4AEE-8F43-C6BB74CD1466&displaylang=en