Can i run l4d with ATI 4650HD AGP on 350w?

The card calls for 400 watt PSU. It should be plenty fast enough for L4D provided the rest of your computer is up to snuff. PSU requirements aren't an exact science and there's often some wiggle room. If your computer doesn't have multiply hard drives, or multiple optical drives, you should be okay, but if the computer just resets itself after when you try to play a 3D accelerated game, then you'll need a more powerful PSU.