Dec 09, 2010 12:05 AM|vijaypant|LINK
Hi for forms authentication, you can obtain the GUID as follows:
'Obtain the currently logged in user as a MembershipUser object.
Dim _user As MembershipUser = Membership.GetUser(User.Identity.Name)
'Obtain the guid of the MembershipUser object.
Dim _guid As Guid = _user.ProviderUserKey
'Use the guid obtained.
testDiv.InnerHtml = _guid.ToString()
But for windows authentication, i don't think so that there is any GUID.