I understand how to put the computer together, but I'm pretty much a noob when it comes to picking out parts for the system. I just wanted to get some feedback for the parts that I selected for my machine. If you think something that I picked is bad please let me know why and suggest an alternative. If you suggest an alternative please try to keep it in the original parts price range. Any and all replies are much appreciated.

DVD Drive - http://www.newegg.com/Product/Product.aspx?Item=N82E16827136134 26.99
 LG Black 20X DVD+R 8X DVD+RW 10X DVD+R DL 20X DVD-R 6X DVD-RW 12X DVD-RAM 16X DVD-ROM 48X CD-R 32X CD-RW 48X CD-ROM 2MB Cache E-IDE/ATAPI 20X DVD±R DVD Burner with LightScribe - OEM

 Case - http://www.newegg.com/Product/Product.aspx?Item=N82E16811129025 139.99
 Antec P182 Gun Metal Black 0.8mm cold rolled steel ATX Mid Tower Computer Case - Retail

HDD - http://www.newegg.com/Product/Product.aspx?Item=N82E16822136178 99.99
Western Digital Caviar SE WD5000AAJS 500GB 7200 RPM 8MB Cache SATA 3.0GB/s Hard Drive - OEM

Video Card - http://www.newegg.com/Product/Product.asp?item=N82E16814102703 89.99
 SAPPHIRE 100218L Radeon HD 2600XT 512MB 128-bit GDDR3 PCI Express x16 HDCP Ready CrossFire Supported Video Card - Retail

Power supply - http://www.newegg.com/Product/Product.aspx?Item=N82E16817139002 169.99
  CORSAIR CMPSU-620HX ATX12V v2.2 and EPS12V 2.91 620W Power Supply 100 - 240 V UL, CUL, CE, CB, FCC Class B, TUV, CCC, C-tick - Retail

Memory  - http://www.newegg.com/Product/Product.aspx?Item=N82E16820231145 109.99
  G.SKILL 4GB(2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1000 (PC2 8000) Dual Channel Kit Desktop Memory - Retail

Processor - http://www.newegg.com/Product/Product.aspx?Item=N82E16819115017 254.99
 Intel Core 2 Quad Q6600 Kentsfield 2.4GHz 2 x 4MB L2 Cache LGA 775 Quad-Core Processor - Retail

Motherboard - http://www.newegg.com/Product/Product.aspx?Item=N82E16813127030 174.99
 ABIT IP35 Pro LGA 775 Intel P35 ATX Intel Motherboard - Retail

heat sink -  http://www.jab-tech.com/Thermalright-Ultra-120-eXtreme-pr-3762.html
Thermalright Ultra 120 eXtreme

120mm fans 2x low speed - http://www.jab-tech.com/YATE-LOON-120mm-Case-Fan-D12SL-124B-UV-Blue-Frame-with-4-Blue-leds-pr-3773.html $10
YATE LOON 120mm Case Fan - D12SL-124B - UV Blue Frame with 4 Blue leds

120mm 1 x MED SPEED - http://www.jab-tech.com/YATE-LOON-120mm-Case-Fan-D12SM-124B-UV-Blue-Frame-with-4-Blue-leds-Medium-Speed-pr-3823.html $5
YATE LOON 120mm Case Fan - D12SM-124B - UV Blue Frame with 4 Blue leds - Medium Speed

You could very well downgrade to a dual core and get the AMD 38x0 or Nvidia 8800/9600GT and get more performance in games. Only if you do quite a bit of video editing/encoding/other CPU intensive and multithreaded programs are you going to see a difference between the dual and quad core.