You can use 3 mobos and 2x7970 graphic card (overclocked)
That is 3 rigs with 2x7970 gpu-s, that should make you around 4 gh/s.
But this is investment, because this cards are little bit expensive.
Bye, M
can u explain a bit how much i would have to invest in total?
and some other info where i could buy those stuffs