How to login into windows when password has national character and keyboard is set to US

• If it is windows 7, then you should have a button on the lower left of the screen. (Actually two buttons. One to shut down without logging in and one to change the locale).
• Alternatively you could log in with another account and change the setting in the registry.
• Or you could boot from a live CD and set the password to nothing. There are a many tools to do this. This is one of them.

Edit: Just saw the new comment stating that it was XP.
The second and third options should still work.