C# Signature:

[DllImport("ntdll.dll")]
public static extern void RtlInitUnicodeString(ref Unicode_String DestinationString,char[] SourceString);

User-Defined Types:

[StructLayout(LayoutKind.Sequential)]
public struct UNICODE_STRING
{
     public ushort Length;
     public ushort MaximumLength;
     public IntPtr Buffer;
}

Sample Code:

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