Oh it'd be entirely legal old chap, I'd be using brand new bought copies of both Win 7 and OSX. I assume (perhaps wrongly) that I could instal Win 7 on one h/d and onstal OSX on the other h/d. The hardware would bought new also so the components could be chosen so there'd be compatibility issues al all (hopefully)
I think you'll find that the hardware will have to be Apple branded. I think thats part of the EULA for OSX.