However, doing a little testing, I found that those of you who have XP Media Center Editions as their OS, have a little power scheme known as "Away". Away is similar to sleep mode and hibernate.
I have found that the away mode still enables MJ to run and saving some power (read $$$$) at the same time. You can do your own search/research on the away mode if it pertains to you.
How to enable/find out if you have this mode:

then

then

If you don't have this option, you may try the hibernate or sleep modes. To date, I have never heard anything positive about the hibernate mode which is why I have it un-enabled on my machines.
I chose to use the any key - on option but you can use it or not.