Could you list out your specs in detail, to help get a picture of what power demands your system would have? 🙂
Power supplies that are not plugged into a motherboard should stay turned off when you plug them in. If they're plugged into a motherboard, then they might turn on when you plug the PSU in, or they might not... it depends on whether the motherboard is configured to power itself up after a power failure or not.
Big picture: if you're building an nForce4 rig with a decent gaming card in it, then a TruePower330 is not really the right tool for the job in my opinion. Something like a 500W Fortron Blue Storm or a 460W Enermax Whisper II 24-pin, now you're cookin' with gas 😀