To configure Power Management on Windows Vista click on Start, Run and then Control Panel.
Control Panel has two views. If you are in Theme View double click on "System and Maintenance"…
…and then on Power Options.
If you are in Classic View simply double click on "Power Options".
Once you are in Power Options you can choose a pre-configured plan, customize one of the pre-configured plans, or create a new plan.
The initial screen for editing a plan allows you to change the monitor and sleep timeout settings.
To change more settings click on "Change advanced power settings". Here you will be able to enable or set values for a variety of Power Management options.
EPA recommends setting computers to enter system standby or hibernate after 15 to 60 minutes of inactivity. To save even more, set monitors to enter sleep mode after 5 to 20 minutes of inactivity. The lower the setting, the more energy you save. The "Turn off hard disks" setting does not save much power, and can be ignored.
PCs may not enter sleep mode when they have a file open over the network. Graphics-intensive screen savers can prevent PCs from entering sleep mode as well, and should be disabled.
Otherwise Vista should not allow software applications to stop it from going to sleep. However, it is possible for a network administrator to change this default, allowing applications to "veto" sleep when they are busy. The default can be changed using Group Policy, but cannot be set through the Power Options applet in the Control Panel.