Questions on my system build/advice

Im buying a new pc in a couple of months and im just trying to figure out everything. Im going to be playing games like cod4, crysis, far cry2, mostly first person shooters. Im stuck with using my 2-3 yearold dell 19inch flat panel monitor but i get to build a brand new pc. I want to be able to play all these games on a good res with no lag pretty much, nice fps u know the works. This is the build i had in mind let me know what you guys think and if u have any advice let me know.

Case - CoolerMaster Centurion 590 RC-590 Mid-Tower

Motherboard - ASUS P5Q Deluxe LGA 775 Intel P45 Intel (price is a little high for a motherboard for me if anyone can help me on finding a good motherboard for about 150 that would be a big help im not planning on doing sli video cards)

CPU - e8500 3.1 1333fsb

videocard - 4850 Overclocked sapphire or the asus brand

memory - anywhere from 2-4 gigs of Dominator 1066

standard hard drive 320gigs

and i was planning on using my windows xp disk I already have but if any1 recommends me upgrading to vista

o ya and 500w powersupply

haha i wont be making a new thread just need to find the right hardware

also the sapphire 4850 i was looking at was like 170ish and had a clock core at 675 and a Memory Clock: 2200MHz, i found another sapphire for 210 and has a clock core of 625 and a memory clock of 1986MHz but instead of 512mb it has 1g, so iono what to do

Well are you planning on overclocking because that will help decide what components you need.

i really dont know how to overclock or do any of that or on what it will do to my stuff lol, wont it make it last shorter? I was just going off benchmark tests that showed the 4850 was good for the price but i might be able to buy the 4870

haha ok well thx for all the help when it gets closer to the time i guess i WILL make another thread since u said u guys really cant help me now since prices will be different