Check for flash

I have an html page with an embedded swf file, that when you click on it it opens my flash site into a centered pop up window, and i would like to have it so when a person visits my site it checks if they have the correct version of flash and if they do not, then it sends them to an html page that i have already made called alternative.html. I have attached the file if anyone would like to look at that and help me out. Thanks a lot. -Ryan.