"From this microsoft kb article on enabling/disabling hibernation:
To make hibernation available, follow these steps:
Click Start, and then type cmd in the Start Search box. In the search results list, right-click Command Prompt, and then click Run as Administrator. When you are prompted by User Account Control, click Continue. At the command prompt, type powercfg.exe /hibernate on, and then press ENTER. Type exit, and then press ENTER to close the Command Prompt window."