I'll put in another vote for Win32::GuiTest, I've used it for automation and it seemed to be the best option.
But... The application that you're controlling has to be brought to the foreground as if you were hitting F8 manually. (GuiTest can do this programatically) I had to use Win32::API to block keyboard and mouse input from the user so they couldn't change focus to another window, or the keypress would go to the new window.
I think this will probably become a problem if you have to do it every few seconds while someone is using the computer.
There could be another way to do it without bringing the window to the foreground, I don't really know. I did this quite a few years ago. At that time, I think there was a yahoo group for questions/support, and I got a lot of help there.
I can post some code if you decide to go this route