The Phenom II x4 945 is on the supported CPU list for the Asus M4A77T See Here but you probably knew that. And yes that board will fit in the Centurion 5 ii case. As for power supplies you need one in the 600W to 750W range, a few suggestions from ebuyer try for a brand name for best reliability but read the reviews they will guide you. You don't mention graphics which will be the most important component in a gaming machine and again you need to check on-line reviews. My only experience is with the ATI Radeon series and in that you will need a minimum of an HD5770. For the operating system I would choose Win7 64bit and put in 8Gb of fast DDR3 RAM
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