This is becoming frequently the norm. Really someone should have checked to see what was being suppled before purchase. if there is a partition with the install files on it that should be ok for as long as the hard disc survives. Instructions should have been supplied as to how to use it.
As regards your second point. You do not own the OS. What you pay for is a licence to use it for as long as you remain within the terms of that licence. If you try to install on another machine you break those terms. So your suppliers are not being unreasonable, and if the hdd does go down you will have to spend serious money to buy a full retail version of Vista if you want to reinstall.