thats right as this guy say, if you have linux you can use a tool named nmap, to scan ports on the net. another powerfull tool its SSH, security shell, if you know the ip adress you can conect via telnet or for some another port...
i.e.

.....# ssh (username)@(ip adress) enter
this is of course if you have a local net, then when you type this its going to ask you for a pass word and then you can conect to the pc, on console mode, but by this way you can do a lot of things with some simple commands like shutdown, reeboot or things like that...

to make a conection with another computer, just read a little of ssh, on internet, google it like this

man ssh

a lot of information comes from about remote conections ok?