Since I'm going to use a USB, I'm not sure which one should I use  Lubuntu or Xubuntu?

I think this is the cheapest I can go so far without using used parts or going diy. Prices vary from day to day, hopefull downward. There are some parts on sale so I have take advantage of those before the sales end.

CPU: AMD Sempron 145 2.8GHz Single-Core Processor  ($35.98 @ Outlet PC)
Motherboard: MSI 970A-G46 ATX  AM3+ Motherboard  ($69.99 @ Amazon)
Memory: Crucial Ballistix sport 4GB (1 x 4GB) DDR3-1600 Memory  ($27.37 @ Newegg)
Video Card: Sapphire Radeon HD 7950 3GB Video Card (2-Way CrossFire)  ($322.98 @ Newegg)
Video Card: Sapphire Radeon HD 7950 3GB Video Card (2-Way CrossFire)  ($322.98 @ Newegg)
Wireless Network Adapter: Encore ENUWI-1XN42 802.11b/g/n USB 2.0 Wi-Fi Adapter  ($9.98 @ Outlet PC)
Case: Rosewill CHALLENGER ATX Mid Tower Case  ($49.99 @ Amazon)
Power Supply: Cooler Master Silent Pro M2 720W 80 PLUS Bronze Certified ATX12V Power Supply  ($74.99 @ Newegg)
Total: $914.26

I did find the intel celeron g550t not the g650t google shopping. They are more expensive than amd chips

Thanks for the clarification, let me take advantage of that sale. I'm going to update the list with the new parts.

I think I can candle Linux I already have a 16 th flash drive. about trying to use older chip versions, I read they are a bottleneck andlower the hash rate of the cards. I haven't bought the parts yet, I'm gathering the money.

For the person that told me to use a milk create, I'm not sure I'm going to have the time to figure out and build a crate for all the parts. Alsomy wife wouldn't like the sight of it

I'm kind of undecided between the gigabyte and saphire vapor x.

Thanks, you are right, I made my calculations with the 7970's I can hash up to 1400Mh/s if oc, with the whole system price of $1100 gives me 1.29Mh/s/$ spent. With the 7950's I can hash up to 1200Mh/s oc, with a price of about $930 for the whole system it gives me  1.27Mh/s/$ spent. So it's not a big difference it saves about $200 dollar, and I added a case with 3 fans.

thanks for the advice, what do you think about this one? it looks pretty good, some what more expensive but I get $40 instant savings plus $25 off mail rebate. I'm going to buy this one first before the the deal ends 5/1, then when I have enough money I'll buy the rest of the gear.

http://www.newegg.com/Product/Product.aspx?Item=N82E16817171067

Thanks, are you saying this because of the brand or the wattage?

I moved this to hardware, since i'm allowed to post there now.

I wonder if the crossfire adapter comes with the graphics card.

This is my update to the list using pcpartpicker.com I might have to ask a friend to invest with me.

http://pcpartpicker.com/user/thehulkk/saved/1wd1

CPU: AMD Athlon II X2 270 3.4GHz Dual-Core Processor  ($53.97 @ Outlet PC)
Motherboard: MSI 970A-G46 ATX  AM3+ Motherboard  ($77.88 @ Amazon)
Memory: G.Skill Ripjaws Series 4GB (1 x 4GB) DDR3-1600 Memory  ($32.97 @ Outlet PC)
Storage: Western Digital Caviar Blue 80GB 3.5" 7200RPM Internal Hard Drive  ($29.99 @ Compuvest)
Video Card: MSI Radeon HD 7970 3GB Video Card (2-Way CrossFire)  ($411.64 @ Amazon)
Video Card: MSI Radeon HD 7970 3GB Video Card (2-Way CrossFire)  ($411.64 @ Amazon)
Wireless Network Adapter: Encore ENUWI-1XN42 802.11b/g/n USB 2.0 Wi-Fi Adapter  ($9.98 @ Outlet PC)
Case: NZXT Gamma Classic (Black) ATX Mid Tower Case  ($29.99 @ Amazon)
Power Supply: CoolMax 700W 80 PLUS Certified ATX12V / EPS12V Power Supply  ($39.99 @ Newegg)
Total: $1098.05

Thanks for the advice, I'll update my list.

lol I'm hoping to get my investment back so I had to empty my savings.

Thanks to everyone that has helped me. I decided to go with the radeon 7950 cards instead of the 7970.  It saves me $200 and with a difference of  0.02Mh/s/$ lower. I made my calculations with the 7970's I can hash up to 1400Mh/s if oc, with the whole system price of $1100 gives me 1.29Mh/s/$ spent. With the 7950's I can hash up to 1200Mh/s oc, with a price of about $930 for the whole system it gives me  1.27Mh/s/$ spent. So it's not a big difference it saves about $200 dollar.  I will use ubuntu 12.04 LTS on a 16 GB thumb drive I already own.

I changed my mind, I will use milk crates, it looks pretty easy to do after reading some guides. Also swiched from msi 970 mobo, to asrock 970 and switched saphire vapor x to xfx.

http://pcpartpicker.com/user/thehulkk/saved/1wd1

CPU: AMD Sempron 145 2.8GHz Single-Core Processor  ($35.98 @ Outlet PC)
Motherboard: ASRock 970 Extreme3 ATX  AM3+ Motherboard  ($74.99 @ Newegg)
Memory: Patriot Signature 4GB (1 x 4GB) DDR3-1333 Memory  ($28.87 @ Amazon)
Video Card: XFX Radeon HD 7950 3GB Video Card (2-Way CrossFire)  ($263.98 @ Newegg)
Video Card: XFX Radeon HD 7950 3GB Video Card (2-Way CrossFire)  ($263.98 @ Newegg)
Wireless Network Adapter: Encore ENUWI-1XN42 802.11b/g/n USB 2.0 Wi-Fi Adapter  ($9.98 @ Outlet PC)
Power Supply: Cooler Master Silent Pro M2 720W 80 PLUS Bronze Certified ATX12V Power Supply  ($74.99 @ Newegg)
Total: $752.77

Hello, I'm back again.  I've decided to build my own mining rig, and for about $800 I included everything I needed with the best graphics card for mining radeon 7970.  I would like some constructive criticism on how can I improve this build for better mining. This is  right in my  budget, but I could expend up to $900.

CPU: AMD Athlon II X2 270 3.4GHz Dual-Core Processor  ($54.99 @ Newegg)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler  ($33.99 @ Newegg)
Thermal Compound: Arctic Silver 5 High-Density Polysynthetic Silver 12g Thermal Paste  ($21.99 @ Newegg)
Motherboard: MSI 970A-G46 ATX  AM3+ Motherboard  ($73.98 @ Newegg)
Memory: G.Skill Ripjaws Series 4GB (1 x 4GB) DDR3-1600 Memory  ($32.99 @ Newegg)
Storage: Seagate Barracuda 500GB 3.5" 7200RPM Internal Hard Drive
Video Card: MSI Radeon HD 7970 3GB Video Card  ($413.98 @ Newegg)
Wireless Network Adapter: TP-Link TL-WN722N 802.11b/g/n USB 2.0 Wi-Fi Adapter  ($15.99 @ Newegg)
Case: Rosewill CHALLENGER ATX Mid Tower Case  ($52.98 @ Newegg)
Power Supply: Raidmax 630W ATX12V / EPS12V Power Supply  ($62.13 @ Newegg)
Optical Drive: Lite-On iHAS124-04 DVD/CD Writer  ($17.99 @ Newegg)
Total: $781.01

So it's the first one, I hope I can give him a good offer.

6850    301.4      1.67    -          2.4    PCI-E 2.0 x16    guiminer / poclbm    -v -f 2 -w 128 clock @ 985 mem @ 890
7950    605    -    -    -    1150    1792    2.6 (10.0.898.1)    PCI-E 3.0 x16    DiabloMiner    GPU: 1150MHz, Memory: 1375MHz; -v 1 -w 256

Thinking about it I can buy the second option since both 6850 will mine as fast as the the 7950, then later replace  or add more graphics cards, what do you think?

I think I'm getting more for the money in terms of harware on the second option, but my goal is to make more bitcoins, so I guess I go for the first option.

I had a good idea that the radeon 7950 was better than the two 6850 combined even if they were overclocled.  Thanks for your input.