can anyone say how to add password to your system when you have a LAN so that others cant access ur computer?

Answer 1

There are several ways:
(1) Put his computer name on your Computer Management (local users and groups -> users). But then if you're using XP all account names will show when you logon and asking for username/passwords. This is good for Windows 2000 & Win2k Advanced Server.
(2) Use firewall like ZoneAlarm, then put his IP on your Firewall tab. In this way, only those IPs on this tab can access your shared folder and also your shared printers.

Answer 2

its called a FIREWALL. get one they prevent unauthorized access to your computer..lol