Recently more and more Office 2007 format file flowing around. If you still prefer to use older version or no money to get the Office 2007 or can't found pirated copy :) then here is a solution for you.
Click on the bottom link, it will bring you to Microsoft website (don't worry, I don't phishing) and download the FileFormatConverters.exe and install. Now you can able to open the Office 2007 files.
It's actually a program that will handle the new file extension (*.docx, *.xlsx, *.pttx) and convert it to previous Office format and open it will old Office application. Sooner or later, we all will need to upgrade to new Micro$oft Office :(
Some information about the latest Office format, basically it's a zipped XML file. If you don't know what is XML then go to this link. If you like to know more about XML for Office, go here
Microsoft Office XML formats
Office Open XML
Welcome to the world of Internet :)