Unsuccessful install - HD Disk Repair - what's the safe/smart way?

Question

Thank you in advance.
I'm trying to update my OS from Leopard to Snow Leopard, but the install is unsuccessful. I have an intel based iMac on which I initially used Tiger and then upgraded to Leopard without any trouble. In the Snow Leopard installation instructions, I read that I should try a few hard drive maintenance measures, but none of those have led to a successful update. Upon trying to verify the disk, Disk Utility reports that the disk does need repair, which is the next troubleshooting step according to the Snow Leopard install guide. Apparently, I can only do so by booting up the computer off an OS installation disc. Naturally, this is a bit disconcerting because I am under the impression that when I repair the disk, it will wipe my hard drive clean; thus, I will have to restore all of my hard drive from a backup or some sort of copy of my iMac hard drive. Unfortunately, I do not fully understand what actually occurs in a hard disk repair and what the potential ramifications are nor do I fully understand what a hard drive restore or re-copying it back to my computer does.
My goal is to update the OS to Snow Leopard so that CS4 is compatible with my computer. Also, I have had trouble using Canon codecs in Final Cut Pro; in fact, I can't even transcode them using the log and transfer option, and I read that an OS update to Snow Leopard may fix the issue. Of course, my ideal scenario is to update the OS while maintaining or easily restoring/copying my iMac Hard Drive volume back to my computer with the updated OS, without having to reinstall apps/software or even redoing all of my preferences or the setup, settings and shortcuts on my desktop and dock. Is this possible? Do you have any suggestions for a better way to go about all of this?
Here are some of my concerns more specifically:
Ordinarily, I try to backup my iMac Hard Drive with QRecall to an external hard drive regularly, but I have never actually had to restore any of the content, thankfully. For the purposes of what I am trying to do, would it be more sensible to just do a drag and drop copy of the iMac Hard Drive volume to an external and then back to the iMac after repairing the iMac hard drive disk and updating the OS or is it smarter to restore from the QRecall archive?
Assuming the hard drive disk repair solves the problem, when should I update the OS, before or after restoring my iMac hard drive? Or is the OS update something that I will do during the iMac hard drive disk repair?
Maybe this is a stupid question, but when I restore or copy (not sure of proper terminology) my current iMac Hard Drive Volume back to my computer, is the old OS not a part of that? Is it possible that I'd update the OS, then restore or copy the hard drive volume back to the computer, and then it would revert back to the older OS Leopard?
Again, thank you very much.

Answer 1

I am under the impression that when I repair the disk, it will wipe my hard drive clean;
That is an incorrect assumption. A disk repair will not erase the hard drive. See:
http://support.apple.com/kb/HT1782
It may, however, be the case that Disk Utility cannot repair the drive catalog. If that occurs, you can try a third-party disk repair tool - Alsoft's Disk Warrior is the one most often recommended - and if that fails then you will have to erase or, if erasing fails, replace the hard drive.
My goal is to update the OS to Snow Leopard so that CS4 is compatible with my computer.
Snow Leopard is not necessary for CS4 compatibility. CS4 predates Snow Leopard by quite a while and is and always has been compatible with 10.5 Leopard. CS5 is necessary for full Snow Leopard support.
would it be more sensible to just do a drag and drop copy of the iMac Hard Drive volume to an external
You cannot do a drag-and-drop backup of your hard drive. There are many hidden files and linkages that would not be copied.
when I restore or copy (not sure of proper terminology) my current iMac Hard Drive Volume back to my computer, is the old OS not a part of that?
Your backup has whatever OS version was on your computer when you made the backup. So if you restore that backup (assuming you backed up the entire drive and restore that same entire drive), you'll be going back to that version of Mac OS X.
I'm complete unclear on when you've made a backup and what got backed up, so without more information I can't say the steps I would take in your situation. Post back with details on your backup and we'll go from there.
Regards.