Yes upping the gpu will give you the best result, can you list what brand and model the psu is? If it is a high quality unit the 5770 will be no problem at all to run. Your mobo doesnt support it???? I dont understand. What mobo do you have, I doubt that it doesnt support win7.
the PSU is the type that came with the mobo, so i think it sucks
my mobo is ASUSTeK P5GC-MX/GBL, it said in asus website that my mobo doesn't support win7 because it doesn't have the driver compatible for win 7 OS. But it support win vista though.
so the cpu doesn't give fps boost?