Vista by default automatically syncs your time to a timeserver (time.windows.com I think), but what your seeing is typically caused by 2 options.
1. Double check your time zone, if your in Central time, make sure your set to 'Central Time (US & Canada)' instead of just 'Central time' or 'Central America'
2. There should be an option in your time settings under control panel to have it 'adjust for daylight savings time', If your in the USA or Canada (which I'm assuming based on the time in your post) make sure you have that enabled.