When you make a wireless network for your home you have the choice to make it a Homegroup or a public network. Naturaly your going to choose the Homegroup and once you do that's where you can find the password on the computer and it works for Vista and XP also as I have had a Homegroup wireless network since XP.
The Homegroup password is stored in it's encrypted form on the computer , if you look in the router it will show you the word or phrase that you put for it to be encrypted , it doesn't show you the encrypted form.
My main desktop is what I used to set up the wireless network and it is coinnected to the wireless router by ethernet cable and the path I posted is where the password is on my computer and where it is on all the computers that are connected.
I hope this answers your question , if not you can always send me a private message and I will be happy to answer any further questions if I can.