請問 如何估計電源供應器瓦數

aopen FSP300-60ATV
asus P4G8X
P4 2.53
DDR RAM 1G
AGP 8X TI4200
WD 80G X1
WD 20G X1
Seagate 120G X2 (SATA RAID1)
AOpen CD ROM
system fan x3
OS win XP(P)