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this site. the P4 you are looking at is about 64 watts that is alot when you want to stay under 150 (for the opus), although there is a 220w opus that is supposidly going to be out soon and that just might do the trick. It is more complicated then just adding up the total watts, you really need to look at the amount of power each device pulls from each voltage rail (for ex. my seagate HD gets power from both the 5v and the 12v) if power consumption on any of the rails exceeds that rails max then it could cause a problem. But looking at the total watts will give you a ball park figgure, and the opus is very effecient and most agree underrated. If you decide to go with a Opus you might want to look at a mobile processor instead of a regular pentium. The pentium M only draws 28 watts for the 2.0 ghz and athlon XP mobile has 35 watt models (like the 2400+)