Need upgrade !!!!

Sup guys,
I would like to upgrade my system to play fairly new/new games at high settings as I got a new monitor with a max res of 1650x1080.I have a max budget of $450-$500.My system is as follows,

CPU:AMD ATHLON X2 6000+
Motherboard:ASUS M3N78-EM
RAM:Corsair value select 2gb DDR2 667
Vid card:Nvidia Leadtek 7600gt
Power supply:Coolermaster Extreme power 450 watts if possible I'd like to keep.

I'm pretty sure the rest of the specs for my system don't need to be told.

I play mostly FPS and racing games.

One last thing, all prices must be in the aus dollar

Thanks guys!!!!!!