If you are running (and rely on) MS Office 2004, it's important that you NOT update to Lion without updating MS Office first.
MS Office 2004 will not run on Lion. It's time to update to MS Office 2011 if you are planning to update your OS to Lion. You can purchase and download MS Office 2011 directly from Amazon.
(Note: The underlying technology, Rosetta, which allowed MS Office 2004 to run on Intel machines, has been discontinued in Lion.)