escape time zone monster

Hi All,
I installed Vista (Dual Boot along with XP). now when I selected Central Time Zone (I am in Chicago), it is showing me +2 Hrs in general (Central Time Zone + 2Hrs). I tried to change it, but of no use.
Now I booted with XP and tried to do the same, it is still showing +2 Hrs. Eventhough I am trying to change, it is not changing and showing me +2 Hrs of current time.
Not sure how to escape from Time Monster. Can anyone help
Thanks in Advance.