for (item = 0; item < numberArray.Length; item++) {
Console.Write(numberArray[item]);
Console.Write('\t');
}
Console.WriteLine();
This section of code actually writes numberArray.Length items in one line and it is the automatic text wrapping of the console that just happens to give you 10 rows of 10 items. The tab width is 8 characters and when the console buffer width is the default 80 characters then wrapping will occur at every 10th tab.
What you should do is start a new line after every N items, where N is the desired number of columns.
Alan.