Advise needed

I all,
I have a Lenovo Think Centre M57. its a nice little machine but I need to make a few changes if possible. It currently has a 280Watt power supply and no Graphics Card .. it uses a Low pprofile-Low Wattage card apparently. What models are are available interms of Graphics Cards and is there a larger power supply as I suspect i will need to upgrade the current 280 Watt aswell. If you can please give me some part/brand/model numbers for the parts I need.

Thanks all