A few things.
-You *can* mix amd and nvidia cards, at least on windows vista/7.
I can confirm that my MB (Asus M4N98TD EVO - http://uk.asus.com/Motherboards/AMD_AM3/M4N98TD_EVO/
) does only work with EITHER AMD or NV card installed.
In this case, doesn't depend on Windows. The problem is in bootup as well.... the PC will boot, but zero video is output to the monitor - can't see it booting, can't see anything, but can hear Windows booting with its "loading tune".
I've tried making sure NV 560 is installed with driver etc first. Then installed 6970 hardware. Upon switching on (with DVI connector still in NV560 card), zero video.
If I uninstalled the 6970 from the board, NV560 springs into life again... behaves as I would expect.
Now I've tried taking out NV560, installing 6970, vwalla..... screen gets video output, works exactly as I would expect it to work.
OK, now this PC of mine is meant for CUDA video processing (which 6970 does not support of course), so will run this 6970 in this PC until I have built "miners rig" for it to go on.
-64 bit OS does make some sense. For 3 GPUs , Im guessing a 32 bit will do, but for 4 or more, you definitely want a 64 bit OS.
-You dont want a quad core cpu. You basically dont need a cpu. Get a single core sempron or whatever is cheapest and lowest power.
-6970 is single GPU (one core). Its the 6990 thats dual.
Most important question; how much do you pay for electricity?
OK thanks, I'll put 64bit Linux onto my mining rig. Its been a long time since I've run Ubuntu Linux! Will be interesting to do it again. Used to be a fanatical Linux fan.
I'm guessing 64bit is needed for supporting more than 4G RAM? Or is it useful also for the Hash processing?
I pay 12p/kwh (UK). I want to start using alt energy sources as well to supplement mains. I'm still not sure how cost effective this whole approach to mining is going to be..... in a way I hope that the value of Bitcoins goes up later!