Hey everybody. I recently installed Office 2008 on my girlfriend's G4 iBook running Tiger. Everything seems to be working well except I can't seem to create charts in Excel. Whenever I click the chart I want on the "ribbon," it spits out the following error:

Cannot open Excel to edit the chart data.

To edit chart data, Excel must be installed. If Excel is
open, make sure all dialog boxes are closed and that
no cells in open workbooks are in edit mode.

I've fished around looking for anything obvious, but I'm pretty new to Macs. No dialog boxes are open when this is happening, and I'm not in the middle of editing a cell when this occurs.

Any help would be greatly appreciated. Thanks!