Caffeine is a utility to keep your Macintosh from going to Sleep with versions for Mac OS X 10.4 or Later
There is a Windows utility that does the same thing: CaffeineCaffeine is a tiny program that puts an icon in the right side of your menu bar. Click it to prevent your Mac from automatically going to sleep, dimming the screen or starting screen savers. Click it again to go back. Right-click (or ?-click) the icon to show the menu.
DESCRIPTION
Caffeine is a tiny program that puts an icon in the right side of your menubar. Click it to prevent your Mac from automatically going to sleep, dimming the screen or starting screen savers. Click it again to go back. Hold down the Command key while clicking to show the menu.
The menu now has a sub-menu for deactivating Caffeine automatically after a number of minutes.
WHAT'S NEW
Version 1.1.1:
* Fixed a bug where Caffeine was effective when another user account was active
REQUIREMENTS
Mac OS X 10.5 or later. A version for Mac OS X 10.4 Tiger is available.
http://lightheadsw.com/caffeine/#introduction