[AccessD] OT: Power Options, Energy Savings, and Heat Control

I  have 3 PCs in my home office. I don't turn them off except when I'm
on vacation. As the  weather warms, I remember how hot my office stayed
last summer (Atlanta area). I'm considering exploring the power options
in WinXP to turn my PCs off between midnight and 7am. 

Does anyone have experience using the power-saving settings?
    
Do the Windows power schemes work well? What versions of Windows? 

How smart is the power off -- will it wake up to start a backup or get
virus updates?

What are the downsides?

TIA,

Myke
The Better Information Group