Why do you want to turn it of for the "Quicktime program" if the error message refers to another program "Windows installer"? And why can't you?
I am running Vista home edition and I'm having trouble every time I try to install or repair Quicktime 7.6.7. It seems to be installing correctly and right at the very end quicktime says that it has finished installing but then I get an error message from windows that says 'Windows installer stopped working and was closed - a problem caused the application to stop working correctly and windows will notify me if a solution is available." When i close that box I get another window saying that Windows DEP has closed windows installer. I have followed the steps in the advanced system settings to modify Data Execution Prevention, but I'm unable to turn it off for the quicktime program. Any ideas on what to do next??