Currently Being ModeratedMay 26, 2012 5:35 AM (in response to asbrookes)
If you have the older versions you will have to upgrade to the Lion compatible versions.
Currently Being ModeratedMay 26, 2012 6:15 AM (in response to asbrookes)
Just to expand on rrfs's answer ... With Lion, Apple dropped the ability to run PowerPC code in emulation mode. They had included this capability as part of the transition from the PowerPC-based systems to the Intel-based systems. People who had been using Office 2004 found that it would no longer run, because it is PowerPC code (versus universal or Intel to run on the Intel platform).
You can buy Microsoft Office 2011, or from Apple you can buy the iWork package or buy Pages, Numbers, and Keynote from the Apple App store, or you can use one of the other office suites like OpenOffice or LibreOffice.