hibernation

Vista/win 7
Control Panel -> Power Options -> Click "Change Plan Settings" (On the plan you have selected)

Then Click "Change advanced power settings"

Click the plus sign by "Power buttons and lid' Set your option appropriately.

Hibernation is a time when animals ‘sleep’ through cold weather. With true hibernation, the animal appears dead. In the Computing, Hibernation is a feature of many computer operating systems where the contents of RAM are written to non-volatile storage such as a hard disk, as a file or on a separate partition, before powering off the computer.

I'm afraid this is probably NOT possible. Hibernation powers down the PC, and standby mode (sleep) puts the CPU at an idle state where very few operations can be done. It would be impossible to run music without waking the PC up. Thats as far as I know.

I think I'd have to agree with Solo.

There is 1 thing you can do, you can close the lid of your laptop without having the laptop 'shutdown', this can be done in power options in your control panel.

There is also a profile where you use less energy >> less performance. This will make your battery usage be minimized.

Furthermore you can disable devices in your device-manager to save power if you don't use these devices.

This is the most reaching possibility to what you want.

You have to have your OS running if you want to listen to music on your laptop, else... get some sort of iPod with internet capabilities

There is also a profile where you use less energy >> less performance. This will make your battery usage be minimized.

Good point, yes I believe in such mode you can turn off both the screen and the hard drive after a certain idle time that you can set, (check the power options in screen saver tab). This will reserve more power as Chojin mentioned. BUT, if your music player uses the hard drive to read say an mp3 file or part of it while it's playing, the HD will power up again and won't shut down until the idle time passes again. Sure, you could set the idle time to a small amount to force the HD to power down frequently, but I don't recommend this, as powering up/down the HD too often might wear out it's mechanics/circuitry on the long run. On the other hand, screen frequent powering up/down probably won't harm it, infact it probably won't happen unless you use the mouse or keyboard.