static extern bool ImpersonateLoggedOnUser(IntPtr hToken);

Declare Function ImpersonateLoggedOnUser Lib "advapi32.dll" (ByVal hToken As Integer) As Integer

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/secauthz/security/impersonateloggedonuser.asp

        blnResult = ImpersonateLoggedOnUser(lngTokenHandle)