Localisation can be controlled at system level or per-use.
To set the system locale, use the System Properties application (there's no web applet) and choose the time zone. This sets all the locale displays including daylight savings. It can also be customised if desired.
For users, they can override their personal locale from the "My Profile" page.
For scripting purposes, try reading this: WebMonkeyMagic: Comparing Dates and Time Zones