Want to build a new pc need help

[Devestion]

My Current rig
Processor-Intel Pentium 4 CPU 3.00GHz (would I have to buy a cpu fan or does that come included when you buy a new one)
Gpu-NVIDIA GeForce 9800 GT(Little side note this used to be my cousins gpu but it over heated and it was unusable blue lines appeared everywhere)
I took it off his hands and baked it now works fine)
Ram 2GB i think there ddr2s
Motherboard-Intel Corporation D945GNT
Monitor Acer AL1916W LCD
HDD I have two of them one is 149GB then 2nd is 232GB
PSU Standard 300w

OK so i want to build a new gaming pc with a price range of 400-500 dollars. There's a couple things i don't really care about upgrading like my monitor,hdds and my cd drives really don't care about upgrading them. I want to get a decent pc which i could play bf3,wow,lol, and pretty much any other game i would like to play down the road without having to suffer fps lag and other performance hindering things. i have a basic understanding of computer things but the amount of different companies and brands really confuse me i cant tell what makes which thing better then the other.

ps. i was thinking of cross firing my gpu with the one you guys recommend.

inb4 tldr sorry about my blabbering

o yeah forgot ill need a new case too nothing fancy tho

[hapylol]

This is what I would do.

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i5-2500K 3.3GHz Quad-Core Processor ($169.99 @ Microcenter)
Motherboard: ASRock Z77 Pro3 ATX LGA1155 Motherboard ($117.55 @ Newegg)
Memory: Mushkin Blackline 8GB (2 x 4GB) DDR3-1600 Memory ($44.99 @ Newegg)
Video Card: XFX Radeon HD 6870 1GB Video Card ($159.99 @ Newegg)
Total: $492.52
(Prices include shipping and discounts when available.)
(Generated by PCPartPicker 2012-05-04 09:20 EDT-0400)

The 6870 is a little lacking in terms of performance on BF3 but it will run WoW/LoL with no problems at all. It should be able to handle medium settings on BF3 though.

You might want to check your PSU and make sure you have ~500W.

[Devestion]

what do you guys think about this build

CPU: AMD Phenom II X4 965 Black 3.4GHz Quad-Core Processor ($109.99 at NCIX US)
Motherboard: ASRock 970 Extreme3 ATX AM3+ Motherboard ($79.99 at Newegg)
Memory: G.Skill Ripjaws Series 4GB (2 x 2GB) DDR3-1600 Memory ($39.99 at Newegg)
Hard Drive: Western Digital Scorpio Black 250GB 2.5" 7200RPM Internal Hard Drive ($59.99 at SuperBiiz)
Video Card: XFX Radeon HD 6770 1GB Video Card ($107.55 at Newegg)
Case: Zalman Z9 Plus ATX Mid Tower Case ($49.99 at NCIX US)
Power Supply: Corsair 500W ATX12V Power Supply ($41.98 at Newegg)
Total: $489.48