validar dni

bool validarDNI( string dni) { if ( new Regex(" [0-9]{8}[A-Za-z] ").Match(dni).Success) { return (" TRWAGMYFPDXBNJZSQVHLCKE "[( int ) long .Parse(dni.Substring(0, 8)) % 23].ToString() == dni .ToString().ToUpper()); } else { return false ; } }

fuente:
http://weblogs.asp.net/aspnet-es-blogs/archive/tags/Trucos/ASP.NET/default.aspx