What do you think bout this gaming rig?A novice need help

HI,I'm novice that need your help.I need your help about this gaming build.Can anyone help me please?Is there any issues about this build?like the voltage,the power,everything.I will accept any opinions.Thank you so much

*Case
NINE HUNDRED)(BLACK) ULIMATE FULL SIZE GAMER CASE

*CPU
(E8400 - 3.0GHZ) (RETAIL) CORE 2 DUO / 1333 MHz FSB / 64-BIT / 45 nm / 6 MB L2 CACHE / SOCKET LGA 775

*Mobo
Asus P5E w/ DualDDR2 1066, 7.1 Audio, Gigabit Lan, 1394, Dual PCI-E x16 CrossFire

*GPU
Sapphire (RADEON HD 4850) (RETAIL) 512MB GDDR3

*Memory
OCZ 4GB PC2-8500 Reaper HPC 4GB Edition Dual Channel DDR2 Kit (2 x 2GB)

*Hard drive
SEAGATE 500GB Barracuda 7200.11 SATA II w/ NCQ, 32MB Cache

*CPU cooler
Scythe Mugen Heatpipe CPU Cooler

*Optical drive
LG (GH22NS30) (OEM - BLACK) 22X SATA DUAL LAYER DVD+/-R/RW

*Power supply
PC Power and Cooling Silencer 750W Quad Power Supply

*Monitor
LG 20" Widescreen LCD Monitor With 2ms Response Time (W2052TQ)

That's a nice PSU, but more than you need. For a single HD4850, 450W is enough. PC Power and Cooling, Antec, Seasonic, OCZ, and Corsair all make good ones.
For RAM, get DDR2-800 that will run at its advertised timings on the JEDEC standard 1.8V. Anything else is a factory overclock, which good DDR2-800 can reach anyway.

I'm going to disagree with jtt283 on the power supply issue.

750W is perfectly fine for what you're doing. Here's the reality. Your motherboard supports ATI Crossfire. If you go with the minimal 450W power supply, you will not have enough juice to add a second video card later if you choose.

Also, 450W might do for a 4850, but your next video card upgrade will want more power than that.

Not to mention, if you buy a GOOD power supply, you should be able to reuse it for a couple of rebuilds in the future. I'd rather spend a little more now, and keep the same power supply for two or three years than replace my power supply every time I upgrade anything else in my system.

As far as RAM. You really don't need more than 800Mhz (PC6400). But the 1066Mhz (PC8500) is getting cheaper all the time. If you don't mind the cost, there's nothing wrong with getting it, and then you don't have to OC it to push your system more.

Again though, 800Mhz is plenty for this current system. Future upgrades will find you with a new motherboard which will likely support DDR3 anyhow.

Since I get Asus P5E with 2x PCI 2.0 x16 slots which will run dual x16 for Xfire,and HD 4850,so I'm thinking to Xfire it within a year,therefore I choose 750W so that I won't change the PSU when I'm going to do Xfire.

I'm sorry that I'm novice about this stuff.Can you explain it clearly to me,please?If OCZ said that the reaper compatible in 2.1V,what does it mean?Will my build able to withstand it?

Does it mean OCZ Reaper that run for DDR2-1066 lose in the performance compare to DDR2-800 memory?I'm planning to overclock my E8400 to around 4.0 Ghz,so is OCZ Reaper good for overcloking?
Before I choose OCZ Reaper,I choose Mushkin HP2-6400 High Performance DDR2 SDRAM (5-4-4-12), 4GB Dual Pack,however I can't buy from online site since I don't have credit card and Mushkin HP2-6400 is currently out of stock in store,so I change to OCZ Reaper.

I will check for it.If the price is still in my budget,I will get 22" instead 20".Otherwise I will stick with 20".Thank you for you suggestions.

I don't want get too many storage since I still have 250GB external hard drive.After all,I get the seagate 500GB for $59.99CAD while it was on sale.WD 640GB AAKS cost $79.99CAD and WD 640GB AALS cost $94.99CAD which the price difference are $20CAD and $40CAD,so I will stick with 500GB seagate.Thank you for your suggestions.I'm really appreciate it

I'm so sorry that the store that I'm going to buy the parts,doesn't sell those memory.
Name of the stores that I'm going to buy the parts are CBit and Memory Express.

I'm totally agree with jerreece about the PSU,that why I choose 750W for Xfire and consider for the future use too.

So what the best timings for DDR2-1066?

Thank you serpent1202,jtt283,MrCommunistGen,jerreece,jugormot and WR2 for all your help so far.