[Tutor] Nested list access?

[Chuk Goodin]

I've got a bit of code here that's giving me some trouble. I am trying
to make a 2 dimensional array with nested lists, but when I try to
change one element, it changes all the elements in that "column".
--begin code--
width = 7
depth = 6

board = [['.']*width]*depth

def printBoard(board):
    'Prints out the 6 x 7 board'
    for i in board: #print board
        for j in i:
            print j,
        print
    return

printBoard(board)
print

board[0][4]='X' #I think this is the line I'm having trouble with

print board
printBoard(board)
--end code--

Here's some of the output in question:

. . . . X . .
. . . . X . .
. . . . X . .
. . . . X . .
. . . . X . .
. . . . X . .

I'm trying to get it to make only one 'X'. Any hints? it feels kind of
like a syntax error on my part...

-- 
chuk