How do i deterministically generate n unique numbers within a range from a GUID?

A guid is effectively a 128-bit number. So you can easily do this provided that the number of bits required to represent your numbers are fewer than the number of bits in the guid (128). You don't need to hash the guid or anything like that.

EDIT:

Now that I know what you need (i.e. a unique seed to be derived from a guid, you could do it this way) - but you could equally hand out a 32-bit number and avoid the guid-to-int conversion.

EDIT2: Using GetHashCode as per suggestion from comments above.

EDIT 3: Producing unique numbers.

 static void Main(string[] args)
 {
     var guid = new Guid("bdc39e63-5947-4704-9e12-ec66c8773742");
     Console.WriteLine(guid);
     var numbers = FindNumbersFromGuid(guid, 16, 8);

     Console.WriteLine("Numbers: ");
     foreach (var elem in numbers)
     {
         Console.WriteLine(elem);
     }
     Console.ReadKey();
 }

 private static int[] FindNumbersFromGuid(Guid input,
     int maxNumber, int numberCount)
 {
     if (numberCount > maxNumber / 2) throw new ArgumentException("Choosing too many numbers.");
     var seed = input.GetHashCode();
     var random = new Random(seed);
     var chosenSoFar = new HashSet<int>();
     return Enumerable.Range(0, numberCount)
         .Select(e =>
         {
             var ret = random.Next(0, maxNumber);
             while (chosenSoFar.Contains(ret))
             {
                 ret = random.Next(0, maxNumber);
             }
             chosenSoFar.Add(ret);
             return ret;
         }).ToArray();
 }