Vista 64 network password/sharing issue

I have a new build with a legit Vista 64 Sp1... my wife has a Dell with a legit Vista 32... I can read, write do whatever to her computer (wireless, private network @ home)... her laptop even sees when I load up Media player...
When I use the laptop to access the desktop it asks for a password. I don't have/know the password. Vista never required one. When I go to Network Sharing "Password" stuff, it WILL NOT change the setting of password protected. I've tried with UAC on and off and nothing.
We are on a private network yet the laptop can see the desktop, can't get onto it. What is my desktop password and/or how do I change it? Why won't vista 64 let me turn off password sharing.
I've done public, private etc etc... nothing works.
I wan't to be able to back-up the laptop onto the desktop during off hours but I can't access it.
Kind of annoying.
Any help appreciated. Best be would be WHAT IS MY NAME AND PASSWORD?
Thanks.