static int[] split(ref int[] array, int len) {
    int[] buffer1 = new int[len];
    int[] buffer2 = new int[array.Length - len];

    Array.Copy(array, buffer1, buffer1.Length);
    Array.Copy(array, len, buffer2, 0, buffer2.Length);

    array = buffer2;
    return buffer1;
}

int[] numbers = {1,2,3,4,5};
int[] begining = split(ref numbers, 3);

foreach (int i in begining)
    Console.Write(i + " ");
Console.Write(" ");
foreach (int i in numbers)
    Console.Write(i + " ");

/* out:
     1 2 3  4 5
*/