is there any unique way to differentiate the login users rather than username and password?.
like the m/c's ip address (not server's address) or something else.
You can check an IP address yes. You can use $_SERVER['REMOTE_ADDR'] for this. More info in the PHP Manual.
Please note that the IP address optained this way is not guaranteed to be unique for your visitors. People behind a NAT router or a proxyserver (as is the case with most offices) will all share the same IP address.
As will anyone on many ISPs who use proxy servers eg AOL, but also me on my new BT broadband link (which is a real pain and will be gone as soon as I can get the b******s to process the change).
The usual solution is a cookie of course.
