This is from Asus Tech Support:
"If the CPU is below 700 MHz, the power supply we suggest as follows:
300 Watts with +5 Volt @ 25 amps, +12 Volt @ 10 amps, and +3.3 Volt @ 14
amps.
If the CPU speed is above 700MHz, the power supply we suggest as follows:
350 Watt with +5V @ 30 amps, +12V @ 12 amps, and +3.3V @ 22 amps.
For Dual Intel MB, Min. P.S. should be:
350 Watt with +5V @ 35 amps, +12V @ 15 amps, and +3.3V @ 22 amps.
For Dual AMD MB, Min. P.S. should be:
400 Watt with +5V @ 38 amps, +12V @ 15 amps, and +3.3V @ 20 amps.
Please note that these are only suggestions and the actual size of the power
supply may be higher than we suggest. Also, depending on the config of your
system, you may need more power than listed above. For example, running
multiple hard drives, CR-Rom drives or other accessories may increase the
power requirements of your system!
Best Regards,
Technical Support Team"
My advice is determine what size you need and buy the next higher size.
Also, pay the extra cash for a quality PSU as it is one of the key elements
of a stable system.
Good Luck,
Koop