I used one program before when I forgot my dial up password, is there a programe like that which can retrieve wireless password / pass-phrase for me ?? Thank you
NirSoft has a variety of password recovery tools, depending on what you need.
(Note: these retrieve the password which you have in your windows settings but cannot see, because it is under asterisks. They do not go cracking wep/wpa protections ... or anything of the sort. For that find specialized tools or linux distributions like BackTrack).
The NirSoft WirelessKeyView tool recommended by Idigas should do the trick for you. If you're using Windows 7, you can view the wireless key without any additional software.
If you have access to the wireless router, you should also be able to reset the router to the factory defaults, and then set a new WiFi passphrase that way.
Personally, I have a piece of paper with the WiFi password taped to the bottom of the wireless router. I figure that, by the time someone's in my house to get that key, I've got bigger problems to worry about than a WiFi passphrase...