In windows xp and lower versions telnet port i.e. 23 is open by default but there comes a need to open it manually in case of windows 7.

Following are the simple steps to do that:

1.Go to control panel

2.programs>programs and features>Turn windows features on or off

3.There just check the Telnet Client  button and thats all.

4.Restart the system.

NOTE: telnet is used for remote login so i advise to keep it open only if you are using it , not just for fun,it can be a wrong decision and you can be very close to be hacked!!!!