Avoid that PSU and instead buy a Corsair CX500W, or 600W good quality PSU's plays a critical role on a gaming system. If possible you may consider a Radeon HD 6870 or newer Radeon HD 7870 card if your budget allows.
that build will give you high settings at 1680x1050 res i guess. a hd 7850 or hd 7870 will be significantly better,but it will also require quad core intel cpus and a quality psu to keep up with the gpu. So for your current settings i guess if you havent bought yet, get a hd 7770, it is still very fresh gpu than ageing gpu such as hd 6850 which is improving performance with continuous driver updates... and also the best part,only consumes max 100 watt, which is easily supported by your psu.