tk623: it definitely does, the drive control board logic requires it.
If you want to run a hard drive off an ATX PSU without a motherboard attached, simply wire pins PS_ON# and any one of the COMs together on the ATX connector (the PS_ON# is normally a thinner green wire and the COM wires are normally black wires) working from this pinout:

EDIT: I'll see if I can wire it together and upload a demonstration picture later today.
EDIT EDIT: you can probably also try picking an AT type power supply out of the trash, you'll find one in any 486 computer or earlier and you won't need to do any wiring. Pretty much any wattage power supply will be enough to run a single HDD.