how do I get logonuser credentials for windows authentication in vb.net?

Not sure what you mean by 'credentials'. In what context, that is. If you mean Windows domain, then you can use the My.User namespace.
You can get the qualified domain username like:
Dim myUser As String = My.User.Name
If you want to see if the user is authenticated:
If My.User.IsAuthenticated Then...
If you are trying work with another users account, you need to use impersonation: http://weblogs.asp.net/ralfw/archive/2003/11/24/39479.aspx 

You can get the user name with domain from "Context.User.Identity.Name"

credentials meaning the user's username from the windows authentication window that comes up to log in to any application.

sort of correct, I had to impersonate the user. Thanks for the help though.