Go to control panel then to Network and Internet then to Network and Sharing cetre then see full map you will get the details of your friend system like IP address, MAC address. Download netcutter software then you can cut their connections. But if you again disconnect and connect to the server you will be able to access the net.
Another way is through Trojan viruses you can download trjan viruses like Girlfriend,Netbus copy that trojan to a CD (as cds are not scanned by maximum users before inserting), you can offer your virused CD to your friend as gift as soon as the CD is readed by your friends system you can gain access of his\her system for that you also need that Trojan virus and you can change his wallpaper send him some warning messages open his CD drive etc.
Apply this only with your close friends.
You can download Netbus from www.packetstorm security.org
