my budget is $850 australian
 
could this handle call of duty 4,bioshock and bf2 high settinging? what about crysis medium settings?
 
im a beginner at this so please tell me if im missing something or need to be aware of something.
 
cpu/processor: amd x2 4800+ (not overclocking) $105 if not in stock 4400+ $95
 
ram: 2x1gb kingston kit 800mhz $65
hdd: 160gb segate sata $66
mobo:ASUS M2N-MX SE $60
 
gfx card: ati 512mb asus x3850 or 8600gts $263/$200 will decide when i get there based on stock and my budget
windows os: xp home $110
Logitech 250 Desktop Keyboard and Mouse, Black (OEM) $15
Optical Drive: ASUS BLT-1814 Lightscribe x18 SATA $42
Case & PSU: Coolermaster Centurion 5 (CAC-T05) w/ 460W PSU $105

any help?

 
With the 8600gts there is no chance of running COD4 at high settings. Also you should really consider opting for a Intel platform. e2140 CPU and Gigabyte DS3 motherboard.

You wouldnt get a high setting system for those games with 850 au budget. 1.2k is probably required to hit high settings.  
 
Im in aus and are also getting a new computer this week. This is what im getting, try make some adjustaments to suit ur budget.  
E2200/E2160 ~$110
8800gt 512 ~$340
8gb 2gb x 4 800mhz ocz ~$320 (bought from america on ebay)  
Antec 900 case ~$160
Antek 500W ~60
Gigabyte DS3 ~140
Segate 500gb ~ 130
Random Optical ~ 40
Zalman 9700 fan ~ 80
 
And why not overclock? Non voltage increase overclock is safe (only if cpu temperature under control). Should be able to hit 50% increase easily on stock cooling, 100% on good fans.

^ not overclocking cause i dont know how
 
also my budget includes a 70 fee fir assembly and 110 for windows which is limiting it
 
my main concern is whether to get a CAC-to5 or thermaltake soprano for the case/psu

I spent 1.5k to get COD4 on high/very high look at my setup obviously I did alot of ocing on everything CPU,GPU,RAM,PCI-E controller.