No way 150W is enough for a P4 set up.
Even the shuttle mini PC's which can only max out 1 optical drive, 1 HD, 1 PCI card, 1 AGP, etc.... and which are HIGH QUALITY PSU's are 200-250W for the P4's
150W is not going to last on a P4 system. And if you have a lot of drives you will probably have instability from a weak/poor power supply.