I'm not sure you'll get 40+ frames in BC2 with a 5770 and your processor. I'm sure others will chime in, but I think I read more than one place that BC2 is optimized for quad cores. This shouldn't dissuade you from trying it out. The 5770 is a pretty darn good card and can run almost anything at your resolution with no probs. And you can OC the 5770 like mad. I've got an xfx 5770, but I've also got an i5 750 and it runs bc2 awesome.
thats a POS power supply. i would not trust it to run a 5770.
as other have stated, BC2 is requires a quad core to run well, as its one of the most demanding titles out there right now.
if you want everything turned on, at that res, you will need the new GPU (and a new PSU for it) as well as a new CPU. it will be a very expensive upgrade if you really want to max the game out and get good framerates.