No such thing as future proofing with pc's, as soon as you leave the shop it will be outdated, but saying that as long as you are not a gamer or into animation or other high load /processing activities you should get 3 years out of it - and 320gig is too small for a hdd, a 500gig sata is only $85 so may add $20 on top of your 320g hdd or budget for a 2nd hdd later on.

