Office 2007 is a Windows version of Office. You can install Windows on that Mac, or you can get Office 2008 for the Mac, or Office 2004 for the Mac, or
http://www.neooffice.org/ if the only reason is to access Word, Powerpoint and Excel. If you need access to Entourage for Mac, that's in Office 2008 or Office 2004. If you need access to Microsoft Access, you will need a Windows operating system installed on your Mac.
See my FAQ* on installing Windows software on your Mac, if it is needed:
http://www.macmaps.com/macosxnative.html#WINTEL
- * Links to my pages may give me compensation.