if you're an experienced overclocker you want to run both OSs - windows to set the card BIOS, and linux to run your miners. that said, 30 Gig HDD is a tad small.
oh - and Rule #1: accept no backorders. difficulty just goes up too damn quick.
quick. like every two weeks or thereabouts. it has recently tended to go up by 50 - 60 % every increase.
Meaning your earnings decrease by 50 - 60 % each time difficulty increases !
it sort of depends on the exchange rate for Bitcoin.
what is the calculable decrease, is your generation rate
, with specific hardware.