More to the point re: power savings -- can you in fact shut down most of the video? --
how much power are we talking about?
I understand that when a high end gpu is loaded up it sucks down power like no tomorrow -- but how much does it burn at idle?
Assuming you don't boot X, can you put the graphics card to sleep pending a keypress?
1. Bios setup through serial console -- the great majority of motherboards do not support this -- but you might try LinuxBios (now known as coreboot)
http://coreboot.org/ supports serial console.
2. A number of non-server Asus "enthusiast" boards do support remote/serial console I believe the A7N8-X did, and a few others - check, you might get lucky.
2. Serial support -- most medium old desktops kept a single serial port on the motherboard -- many systems didn't pin these out -- but check your manual and scrounge for old serial header to d-sub slot fillers.
3. People mentioning laptops re: lack of serial ports -- this is a discussion about headless desktops -- keep your mind on the problem and solutions and stop spitballing -- laptops don't go headless.
4. If it's a desktop without serial ports put in an add in card. Hopefully a common one that the kernel and grub will both be able to see (and presumably coreboot if you go that route for bios level serial)
I would not recommend trying to work out USB -> Serial for your console -- you'll almost certainly not be able to make it work with grub (pending some savant deciding to add PL203 support to grub)
Again -- how much power are you saving by going absolutely headless? Did you measure? I've generally assumed load from AGP card at rest is minimal -- am I wrong?
- Jeff Dodge