Are talking about a silent install while the user is browsing your website? That sounds like unwanted software to me!! and users do not really like to have that!!
If you are talking about a normal application installation, the user will still have to clieck some executable file to start the installation.
Also beware that in some countries, installing unwanted software on the pc of others without prior acknolegments could lead to legal actions, so I sugest informing the user of what is happening.
Regards,
Sim085