Need Help with my first build, phenom II X 3 720 budget gaming/home PC

Hello All,

I am looking to Spend between $600 and $700, not including monitor.

APPROXIMATE PURCHASE DATE: Hope to have the whole thing purchased within the week. bye the weekend

SYSTEM USAGE FROM MOST TO LEAST IMPORTANT: Gaming, entertainment (movies, music, possible HTC in the future) surfing, home/work use. I really need a decent all around computer that can handle gaming. Did gaming years ago and would like to get back into it.

PARTS NOT REQUIRED: keyboard, mouse, speakers, OS. CPU, I just picked up my Phenom II x 3 720 Black box addition at Micro Center for 99.99

PREFERRED WEBSITE(S) FOR PARTS: Newegg, primarily as well as micro center.

PARTS PREFERENCES: Already have the processor, leaning towards a gigabyte MOB, and radeon video card.

OVERCLOCKING: Hopefully once I get my feet wet an get more comfortable with computers. So would like to have the potential to, maybe even trying to unlock that fourth core.

MONITOR RESOLUTION: Haven't gotten that far yet.

ADDITIONAL COMMENTS: A little background. I used to be fairly knowledgeable of computers but have found myself quite behind on what has been happening. My last computer purchase was over 5 years ago, an HP laptop after my previous (friend) built system got fried. I am typing from said HP. Needless to say my AMD Athlon 64 3200 with 512MB is way over due to be put out of her misery. I have no idea how it has lasted this long.

With that being said I need some help and have been spending the better part of the past three days glued to this site (and others) trying to catch up and figuring out what I need/want and think I have done a pretty good job.
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I am building the system around the Phenom II x 3 720 Black Box addition which was purchased this evening.

Here is what I have been looking at so far:

MOBO: GIGABYTE GA-MA770T-UD3P AM3 AMD 770 ATX AMD Motherboard - Retail
http://www.newegg.com/Product/Prod [...] 6813128392

HD: Western Digital Caviar Black WD6401AALS 640GB 7200 RPM 32MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive -Bare Drive
http://www.newegg.com/Product/Prod [...] 6822136319

GPU: SAPPHIRE 100245HDMI Radeon HD 4850 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFireX Support Video Card - Retail
(limit 99 per customer) what's this?
http://www.newegg.com/Product/Prod [...] 6814102824

PSU: Antec NEO ECO 620C 620W Continuous Power ATX12V v2.3 / EPS12V 80 PLUS Certified Active PFC Power Supply - Retail
http://www.newegg.com/Product/Prod [...] 6817371031

Case: Antec Three Hundred Illusion Black Steel ATX Mid Tower Computer Case - Retail
http://www.newegg.com/Product/Prod [...] 6811129066

Other Possible cases:

COOLER MASTER RC-690-KKN1-GP Black SECC/ ABS ATX Mid Tower Computer Case - Retail
http://www.newegg.com/Product/Prod [...] -_-Product

memory: This is where I have hit a wall. There are a lot of options, I am looking at 4Gbs of ram for around $100, thinking DDR3 since there doesn't seem to be that much of a price difference with DDR2

DVD: Also not really sure, looking to spend between $20 and $30.

Monitor: I am looking for something between 21.5" 23". From what I have read Acer does a pretty good monitor. It also looks like I can expect to spend between $150 and $200 on the monitor, which is what I have put aside for my monitor budget which is not included in my original build budget.

I would greatly appreciate any input, recommendations and advise on what I need to do, especially since this is my very first build I am doing myself, and am quite the "newbie".

Thanks for your help.