oh I see.. i didnt know u meant downgrade the processor... i thgouth u meant less gpus
so whats the bare minimum in parts i need to build a rig....
4. linuxcoin off usb (how do i get one of these on the usb? dl on other cpu and put on a usb stick than transfer to dedicated rig?)
1. processor AMD Sempron (or Athlon II x2 if you want a little more power)
2. PSU A good 850w unit. Corsair or Seasonic are good, and the prices are reasonable. The Corsair HX850 is great.
3. GPU I thought you had already settled on 4x5850. Keep in mind that 5850s are pretty efficient. If you go with 6950s instead, you probably do want a more powerful PSU, though I wouldn't be surprised if the Corsair HX850 could handle them. According to hardwaresecrets.com, that PSU is better than many 1000w units.
4. linuxcoin off usb (how do i get one of these on the usb? dl on other cpu and put on a usb stick than transfer to dedicated rig?) Do a forum search for linuxcoin and you will find instructions. Another option for a dedicated rig is BAMT, which might be easier to get started with (again forum search bamt).
5. Any mobo that has 4x pcie 2.1 or 2.0 slots. The cheapest way to go here is with a mobo that has two standard slots (typically 1 will be x16 bandwidth and the other x4 or x8). The other two slots will be x1 bandwidth and you won't be able to plug the card directly into it. Instead you will need ribbon cable extenders. You should just get ribbon cable extenders for all the cards so you can spread them out above the board for good airflow. As I said, the Biostar A870u3 is one option here, but I think there is also a cheap gigabyte board that will work too.
6. 4x extender cables. Cablesaurus on ebay sells these I think. I haven't actually done this, just know it can be done, so you will have to track down the relevant info. You will need two to fit the x1 slots on the board, and 2 to fit the normal slots.
7. USB stick (obviously)
8. Cheap house box fan to blow across the rig
9. A power switch? If you search for "test bench power switch," that should get you to what you need. But you can actually just short the power leads on the mobo with a small screwdriver to start the rig (all the switch does is short the leads anyway). See the link below, which has some pics of caseless rigs, and I think there is a discussion of what to do to power on further down in the thread:http://forum.bitcoin.org/index.php?topic=27496.0
10. I think that's it, but I might be forgetting something. Obviously this route will take more research on your part than a standard build, but you can save $ this way. Beyond the GPUs, you can probably get everything else for $250 or so.