I'd explain to him that He should be paying for the new gear anyway. If he'd taken the computer to a shop, they'd charge for the time too. It's not *your fault* his POS died in your arms. You didn't cajole him into upgrading his hard drive and you were doing the right thing by offering to help.
If he has any decency he'll offer to pay for the parts anyway. if he doesn't, just hand if back and appologise that he should have taken it to a shop if he wanted things done for free.
I don't mean to be offensive, but you aren't profiting from this and he's actually getting a good deal.