$600 gaming pc

[edited thanks for the reminder KageRyu  ]
I was wondering if you guys can help me with my first build.

I'll be purchasing the unit on the end of april and my budget for the rig would be $600 maybe less if the
lcd monitor is included as well.

I'm going to use this for gaming... (mass effect 2, crysis, far cry 2, and the list goes on... )

i already have an atx casing, a 500w psu a keyboard and mouse, a 40gb and 120gb IDE hdd though would be
willing to buy a sata hdd if there is a little more left.

i really don't have any preferred website for the parts, though what i'm sure is that i'd be going amd-ati for my proci and gpu

i'd like to try some overclocking but i wouldn't mind if the board cannot handle crossfire

i'm planning on buying an lcd monitor in place of my crt monitor as well...  

and there would be no airconditioning whatsoever in my place...

so far base on what i read a phenom II x2 555 be would suffice for my processing needs (http://www.tomshardware.com/reviews/best-gaming-cpu,257...)

and a sapphire hd5770 vapor-x would guarantee that i'd be able to play those titles  


here is basically what i'm planning so far:

proc: phenom II x2 555 be($101)
- http://www.newegg.com/Product/Product.aspx?Item=N82E168...

mobo: any good mobo that'd allow me some OCing

ram: any 2x2gb ddr3 kit

gpu: sapphire hd5770 vapor-x ($175)
- http://www.newegg.com/Product/Product.aspx?Item=N82E168...

so far that's $276 and that would give me $324 for my mobo, ram and hopefully an lcd monitor *sigh* I really hope this build can push through...  

thanks for the help in advance!