If you don't see the option under your start menu, don't panic.
1. Run the command prompt as administrator.
2. Type "PowerCfg /a" to see if your computer supports this feature (look for S3 for hibernate)
3. If this option is available, at the command prompt, type PowerCfg /hibernate on.
Enjoy :)
MSKB Article 929658
http://support.microsoft.com/default.aspx?scid=kb;en-us;929658