I would like to put a graphics card in my PC to be able to play games like Team Fortress 2, Microsoft Flight, APB Reloaded, and other Steam games all with good framrates and higher settings. I realize that the power supply is small so would that need an upgrade?
Motherboard: MSI MS 7548 AM2+
CPU: AMD Pheonom X4 9550
RAM: 6GB DDR2 800 MHz
Your phenom is an older model that is not a good performer , and it also wont overclock well .
It may be possible to improve gaming performance with a graphics card , but you will be limited to cheaper less powerful models.
Something like a Radeon 6770 might work , but you would need to change the psu to a 450 watt unit
What is the resolution of your monitor ?