Change the keyboard layout at the login window
Mac OS X v10.4 or later
1.From the Apple menu, choose System Preferences.
2.Click Accounts to display the pane (or choose Accounts from the View menu).
3.If the lock icon in the lower-left corner of the window is closed, click it, then enter the name and password of an administrator to unlock it.
4.Click Login Options.
5.Select the “Show Input menu in login window” checkbox.
6.From the Apple menu, choose Log Out.
7.At the login window, click the name or flag icon of the currently selected keyboard layout (it appears below the name of the computer), then select the desired keyboard layout. If you don’t see the keyboard layout you are looking for, move the pointer over Other Sources, then select the keyboard layout from the complete list that appears.
Mac OS X v10.3.9 or earlier
1.Enable the root user. To learn how to do this, see “Enabling and using the ‘root’ user in Mac OS X”.
2.From the Apple menu, choose System Preferences.
3.Click Accounts (or click Login if you use Mac OS X v10.1.5 or earlier).
4.Click Login Options (or click the Login Window tab if you use Mac OS X v10.1.5 or earlier).
5.Next to “Display Login Window as,” select the “Name and password” option if it isn’t already selected.
6.Quit System Preferences.
7.From the Apple menu, choose Log Out.
8.Log back in to your computer by typing root in the Name field.
9.Enter the password you used when enabling the root user, then click Log In.
10.From the Apple menu, choose System Preferences.
11.Click International to display the pane.
12.Click the Input Menu tab.
13.Select the checkbox next to the desired keyboard layout or input method.
14.Scroll through the list and deselect the checkbox (remove the check mark) next to all unwanted keyboard layouts and input methods. If more than one keyboard layout is checked, you must choose the one you want to use at the login window from the input menu on the menu bar.
15.From the Apple menu, choose Log Out.
Source : http://support.apple.com/kb/HT4099