Here I saw that.
by R. Proffitt - 1/21/13 1:01 PM
In Reply to: Flash Player Doesn't Complete Installation on Windows Vista by g.no
It turns out it was waiting for me to close my browser and email apps. Try this. Reboot and do not run the browser or email. Try again.
No Go? Try Chrome as it has flash built in. And keep in mind that some of today's security apps lock out add ons. Flash is a web browser add on.