Hi !
Don't worry, your new PSU will be quite enough.
Just look at this :
http://www.matbe.com/articles/alims/hiperr/page6.php
It's made by a Belgian community which writes in French, so, you might be able to understand most of the article, but what you have to keep in mind is the biggest number of Watts.
That's the peak of consumption of the machine, when you take in account the efficiency of the PSU.
The worst PSU gives us 368W for an overclocked system, and take a look at the specs :
Processeur Intel Pentium 4 560
Carte mère Asus P5AD2 Premium
2x512 Mo de DDR2 Corsair PC-5400 (667 MHz)
Carte graphique Abit X600 XT
2 disques durs Western Digital Raptor 74 Go en RAID
It's a Pentium 4 Platform, with the Prescott core, which has a reputation to be the leader for the waste of energy.
So, 368W is the consumption when you take into account the efficiency. Let's imagine that the best PSU has an utopic 100% efficiency. In this case, it would mean that the system pumps a maximum of 309W.
Since the number of Watts on the PSU is nearly a guarantee that the system can take this number of Watts, there will be no problem, since the 309W PSU gives less Watts to the system.
And for heaving read tons of articles, I can guarantee you that a 350W PSU is enough for your PC.
If you can, I although recommand you a 330W or 380W PSU of Tagan ; I discuss of the sound of these PSUs with my mates at
www.pcsilencieux.com nearly every day, and they find it wonderful. And something else that is important, the Belgian article that I gave you has compared a few brands of PSUs, including a Tagan ; when you watch the consumptions, you see that the Tagan is very efficient, just a bit behind the passive-cooled PSU Phantom from Antec, which costs too much.
I hoped I was clear enough.
See you
)