I find that if your HDD won't boot and it isn't because of a software change that recovering the HDD isn't worth it because it is likely that another sector of the HDD will fail or Windows just won't install properly.
I've found that the easiest way to save your data is to boot with a linux Live CD (Knoppix would work) and copy everything to an external HDD. Once done, install a new HDD, install windows, and copy everything back to your new drive.
Having luckily survived situations like this a few times myself I developed a backup plan that wasn't too expensive and is easy enough for me to follow (since it is mostly automatic with the exception of imaging my OS).