Hibernate basically copies the actice RAM to the HDD and shuts down, saving the system state. So HIBERNAT.SYS will be equal to the amount of physical RAM you have in the computer.
And for clarification, the Hibernation shuts the PC completly down, standby olny puts it into a reduced power state. Modern computers will still have all the fans and stuff running whe in standby mode, therefore not conserving much power anyway. Hibernation reduces power usage to 0 and shuts the machine completly off, but allowing you to restore your session to where you left it
JJB