Pretty much anything with a motor uses 12 volts. So, add up the power that everything uses, like you mobo, the fans, the HDs, ect, and see how that stands against your power supply's maximum rating.
Still weak, I know, but getting better:
CPU: AMD AthlonXP 2500+
1.8GHz @ 333 FSB
512 DDR 2700
160 GB westerndigital hd
Dual booted with XP/Fedora Core 5
PCchips M848A mobo
nVIDIA GeForce MX 4000 video Card
Associate\'s Degree in Applied Computer Sciences.
A+ Certified for Hardware and Operating Systems. Network+ Certified