simple tic tac toe gone wrong

[mytruehate]

i will start off by saying yes this is for school, but i have gotten myself hopelessly tangled in the code. i am not looking for the answer but some help would be lovely. i know its simple code, but i am very new.

what i am trying to do is make a multilayer tic tac toe game, with the option to play against the computer (not intelligently, the computer goes at random.) or another person.

// Tic Tac Toe, by: Travis Litton

// Included libraries
#include <iostream>
#include <string>
#include <ctime>

//Used namespace
using namespace std;

// Declared global variables
char Board[9];

// Declared functions
void showBoard ( );
bool moveIsValid (int m);
int whoWon ( ); //Returns 0 if no one has won, 1 if player 1 has won, and 2 if player 2 has

void main ( )
{
	// seed the random number
	srand (time (NULL));

   // Declare local variables
   string Player_1_Name;
   string Player_2_Name; 
   int Whose_Turn = 1; // 1 = player 1's turn, 2 = player 2's turn,
   int Move; // Stores where the player wants to move
   int Total_Moves = 0;
   int Cmove = rand ( ) % 8;
   int Player_amount =0;

   //Assign values to the playing board
   Board[0] = '0';
   Board[1] = '1';
   Board[2] = '2';
   Board[3] = '3';
   Board[4] = '4';
   Board[5] = '5';
   Board[6] = '6';
   Board[7] = '7';
   Board[8] = '8';

   // Get number of players
   cout << "please tell me how many players we have today." << endl;
   cin >> Player_amount;

   if (Player_amount == 2)
   {
	   // Get player names
	   cout << "Player 1: Please enter your name." << endl;
	   cin >> Player_1_Name;
	   cout << "Player 2: Please enter your name." << endl;
	   cin >> Player_2_Name;

	   while (whoWon ( ) == 0 && Total_Moves < 9)
	   {
		  // Do this until the player chooses a valid move
		  do
		  {
			 // Show the board
			 showBoard ( );

			 // Tell which player to move
			 if (Whose_Turn == 1)
			 {
				cout << Player_1_Name << ": It's your turn." << endl;
			 }
			 else
			 {
				cout << Player_2_Name << ": It's your turn." << endl;
			 }

			 // Get the move
			 cout << "Enter the number of the spot where you'd like to go." << endl;
			 cin >> Move;

		  } 
		  while (moveIsValid (Move) != true);

		  // Add 1 to Total_Moves
		  Total_Moves++;

		  // Change whose turn it is
		  switch (Whose_Turn)
		  {
		  case (1):
			 {
				Board[Move] = 'X';
				Whose_Turn = 2;
				break;
			 }
		  case (2):
			 {
				Board[Move] = 'O';
				Whose_Turn = 1;
			 }
		  }
	   }
	   // Show the board
	   showBoard ( );

	   if (whoWon ( ) == 1)
	   {
		  cout << Player_1_Name << " has won the game!" << endl;
	   }
	   else if (whoWon ( ) == 2)
	   {
		  cout << Player_2_Name << " has won the game!" << endl;
	   }
	   else
	   {
		  cout << "It's a tie game!" << endl;
	   }
   }

	else
	{
		// Get player name
	   cout << "Player 1: Please enter your name." << endl;
	   cin >> Player_1_Name;


	   while (whoWon ( ) == 0 && Total_Moves < 9)
	   {
		  // Do this until the player chooses a valid move
		  do
		  {
			 // Show the board
			 showBoard ( );

			 // Tell which player to move
			 if (Whose_Turn == 1)
			 {
				cout << Player_1_Name << ": It's your turn." << endl;
			 }
			 else
			 {
				cout << "It's the computers turn." << endl;
			 }

			 // Get the move
			 if (whose_Turn == 1)
			 {
			 cout << "Enter the number of the spot where you'd like to go." << endl;
			 cin >> Move;
			 }
			 else
			 {
				 cout << "Enter the number of the spot where you'd like to go." << endl;
			 cin >> Cmove;
			 }
		  }
		  
		  while (moveIsValid (Move) != true);

		  // Add 1 to Total_Moves
		  Total_Moves++;	 

		  // Change whose turn it is
		  switch (Whose_Turn)
		  {
		  case (1):
			 {
				Board[Move] = 'X';
				Whose_Turn = 2;
				break;
			 }
		  case (2):
			 {
				Board[Move] = 'O';
				Whose_Turn = 1;
			 }
		  }
	   }
	   // Show the board
	   showBoard ( );

	   if (whoWon ( ) == 1)
	   {
		  cout << Player_1_Name << " has won the game!" << endl;
	   }
	   else if (whoWon ( ) == 2)
	   {
		  cout << Player_2_Name << " has won the game!" << endl;
	   }
	   else
	   {
		  cout << "It's a tie game!" << endl;
	   }
	   }
	   system ("PAUSE");
}
	void showBoard ( )
	{
	   cout << endl;
	   cout << Board[0] << " | " << Board[1] << " | " << Board[2] << endl;
	   cout << "--+---+--" << endl;
	   cout << Board[3] << " | " << Board[4] << " | " << Board[5] << endl;
	   cout << "--+---+--" << endl;
	   cout << Board[6] << " | " << Board[7] << " | " << Board[8] << endl;
	   cout << endl;
	}

	bool moveIsValid (int m)
	{
	   if (Board[m] != 'X' && Board[m] != 'O')
	   {
		  return true;
	   }
	   else
	   {
		  return false;
	   }
	}

	int whoWon ( )
	{
		//win across
	   if (Board[0] == Board[1] && Board[1] == Board[2])
	   {
		  if (Board[0] == 'x')
		  {
			 return 1;
		  }
		  else
		  {
			 return 2;
		  }
	   }
	   if (Board[3] == Board[4] && Board[4] == Board[5])
	   {
		  if (Board[3] == 'x')
		  {
			 return 1;
		  }
		  else
		  {
			 return 2;
		  }
	   }
	   if (Board[6] == Board[7] && Board[7] == Board[8])
	   {
		  if (Board[6] == 'x')
		  {
			 return 1;
		  }
		  else
		  {
			 return 2;
		  }
	   }
	   //win down
	   if (Board[0] == Board[3] && Board[3] == Board[6])
	   {
		  if (Board[0] == 'x')
		  {
			 return 1;
		  }
		  else
		  {
			 return 2;
		  }
	   }
	   if (Board[1] == Board[4] && Board[4] == Board[7])
	   {
		  if (Board[1] == 'x')
		  {
			 return 1;
		  }
		  else
		  {
			 return 2;
		  }
	   }
	   if (Board[2] == Board[5] && Board[5] == Board[8])
	   {
		  if (Board[2] == 'x')
		  {
			 return 1;
		  }
		  else
		  {
			 return 2;
		  }
	   }

	   //win diagonally
	   if (Board[0] == Board[4] && Board[4] == Board[8])
	   {
		  if (Board[0] == 'x')
		  {
			 return 1;
		  }
		  else
		  {
			 return 2;
		  }
	   }
	   if (Board[2] == Board[4] && Board[4] == Board[6])
	   {
		  if (Board[2] == 'x')
		  {
			 return 1;
		  }
		  else
		  {
			 return 2;
		  }
	   }
	   return 0;
	}

1st i wrought out the 2 human player version biased on notes and such from class and that all went well. i still have the version 1 code backed up, but then there is a second grading rubric that says:

Computer_Tic_Tac_Toe Grading Rubric Points            possible Points earned
Computer_Tic_Tac_Toe.cpp includes the ctime library.      2.5
Computer_Tic_Tac_Toe.cpp has the srand ( ) and rand
 ( ) functions in it.                                     2.5
Computer_Tic_Tac_Toe.cpp has one % operator in it.        2.5
In Computer_Tic_Tac_Toe.exe, the computer moves for 
player 2, instead of asking player 2 to move.             2.5
Total points earned                                       10

and biased of that rubric i have been twisting and editing the code since yesterday...

all i am really asking is:
1.could someone could point me in the right direction for making player 2 an optional "A.I."
2.where did i go wrong?
3.suggested help site for newbie debugging, and learning.