"Hi there , im also running 5 shaman on a quadcore q6600 one harddrive and 4 gig of ram ...
Its runs perfect exept if i went to shattrath.
Same as you here , lose grafiks , wow error (that destroyed the whole wow) and low fps...
Result was ram was not ok ..... switched the ram and everything is ok .. no wow error
Still got lags and low fps in shatt "

So you increased your memory and switched to Win Vista? or your memory was bad.
I will probably get the extra hard drive and memory together when I can afford it