Acrobat standard upgrade

I'm trying to upgrade to Adobe 8.0 standard from Adobe 6.0 standard. When i try to uninstall 6.0 i get a window saying "The installation source for this product is not available. Verify that the source exists and that you can access it" I have tried to re-install 6.0 and i get a window saying "the installation source for this product is not available. verify that the source exists and that you can access it" i have also tried to uninstall 6.0 through the 8.0 install and that failed. I have tried to update 6.0 thinking that would help and the updates fail. Short of re-formating the hard drive, is there a solution that will allow me to uninstall 6.0? Thank you for your help.