Upgrading old gateway gt5676

[Vengeful]

Trying to upgrade tower to best gaming tower it can possibly be. So, i have an old gateway gt5676 which is decent except for the graphics card. I was thinking of adding a nvidia geforce gtx 670 superclocked gpu to the open pci-e slot which would require me getting a new PSU correct? I was thinking of adding a seasonic m12 700w power supply but i was unsure if it would fit or not. Also, i was thinking of changing the cpu to a phenom x4 9850. do you think this would be enough to make it an acceptable gaming computer? The current cpu is an AMD Phenom X4 9600, the current video card is an ATI Radeon HD 3200 and the power supply is 300w.

 

[Vengeful]

How about changing the motherboard out for a Biostar TA785GE 128M 6.1 to put a Phenom II X4 965 125W AM3 Processor in? Anyone with any insight?