the case is like this,

I have a application program,
I need the user to used it while they online...

so...
user will browse my website...
inside my website, I should have something to check the user side have my application program or not... if not, then they need to download it.

my problem is, how can i detect users side whether they had install my program?

my friend had told me to create an active X to do that... but I'm no idea at all...

any help?
tutorial?