Promise Raid

hello; i am planning to get gigabyte gtx 560 graphics card, but everyone is telling me: "be sure to have a powerful psu" , right now i am planning to put it alone on a good brand 200w psu as on gigabyte web site says it requires 150w , is this enough or should i do something else ?! thanks in...

I have a Pavilion a4327 PC, AMD Athlon ll 240 dual core, 4GB, GeForce 6150SE nForce 430, main: M2N68-LA (Narra5), power supply: ATX-250-12Z REV D7R 250W. I want to upgrade my graphic card to Radeon 5570 1GB DDR3 128bit cause it doesn't need a lot of power and have a good performance. And I don't...