Website Re-Direction

So I have heaps of available PCs to use for servers etc. and i'd like to know that, when someone comes over, how can I always redirect their URL searches etc. to a site that I host (say, 192.168.1.25) unless they have a "client" installed? (The site has the Client on it)

The client would connect to the server (192.168.1.25) and that server would also be the default gateway that checks if there is a client on the incoming IP? Is this possible? I know that products like CyberHound re-direct to a certificate installation website for SSL sniffing so how do they do this?

Thanks,

Duffy