Sorry you are having difficulties, Bravozulu. The spreadsheet has been tested on Excel 2007 for Windows and Excel 2004 (and later editions) for Mac. However I do not know about your G4 which I think was PPC based and does not have an Intel Processor and that may be the problem. It's all the conditional formatting and data validation that your CPU can't handle.
If so, I'm afraid there is no way around it, as you wont be able to run the Numbers version either - looks like a new computer ..., ouch!!
When words become unclear, I shall focus with photographs. When images become inadequate, I shall be content with silence. - Ansel Adams