if i were going to do this i would use a laptop HDD due to the fact they are built for shock more than desktop types... for heat disipation i'd probably stick some chipset heatsinks or the old 486 ones to the lid if it makes any difference and maybe a directed fan aimed totally on the underside... for the spinggy ness... maybe use something like 10 springs or elastic band type things at the corners and the side... this should deal with most knocks... or you could canibalise some of those gel wristrests... and put it all ways round to pad it in and make it secure.
