I cannot open an excel file because I get an error code that says "The file might have been damaged or modified from its original format". How can I open this very important file?
You can try this, down the page you will see it states that it improves stability and resolves the issue you cited: Description of the Microsoft Office 2008 for Mac 12.1.3 Update
http://support.microsoft.com/kb/958267 (under the heading "Improvements for Microsoft Excel 2008 for Mac")
iMac G5 1.8GHz "Hero" PowerPC
2 x 1GB DDR PC3200 SDRAM
160GB WDC WD1600JD-40GBB2
Mac OS X Leopard Version 10.5.8