If you want to play with new software, you're gonna need new hardware.
Overclock the crap out of the quad core. The ATI 5770 is complete fail, try upgrading that first. Ram is cheap now a days, so there is no reason not to upgrade that to 8gig.
If it's that bad for you, and you don't want to upgrade the hardware, try playing some older flight titles. Comanche 4 by Novalogic is an awesome helo game - your machine will rock it with no problem. I use to play that game a lot back in the day.