C# Signature:

[DllImport("ntdll.dll")]
public static extern void RtlInitUnicodeString(
  ref UNICODE_STRING DestinationString,
  [MarshalAs(UnmanagedType.LPWStr)] string SourceString);

C# Signature:

[DllImport("ntdll.dll")]
public static extern void RtlInitUnicodeString(
   out UNICODE_STRING DestinationString,
   [MarshalAs(UnmanagedType.LPWStr)] string SourceString);

Boo Signature:

[DllImport("ntdll.dll", SetLastError : true)]
def RtlInitUnicodeString(ref DestinationString as UNICODE_STRING, [MarshalAs(UnmanagedType.LPWStr)] SourceString as string):
     pass

User-Defined Types:

public struct UNICODE_STRING
{
     public ushort Length;
     public ushort MaximumLength;
     [MarshalAs(UnmanagedType.LPWStr)]
     public string Buffer;
}

[StructLayout(LayoutKind.Sequential, Pack : 0)]
struct UNICODE_STRING:
     Length as UInt16
     MaximumLength as UInt16
     Buffer as IntPtr

User-Defined Types:

UNICODE_STRING

Sample Code:

http://www.rootkit.com/vault/hoglund/migbot.zip