Whoa boy, here we go:
1. No idea. I've never had that problem myself.
2. OSX comes with QuickTime 5. There is no need to update. Minor updates can be handled through the Software Updater.
3. An extension is a modular program which is loaded upon startup; they add functionality to the system.
At startup they're loaded into memory as a part of the system; however, they do not occupy any part of the system heap - they use their own memory space, and act like invisible processes.
4. Yes, back up - you must erase the hard drive and re format it. Use the Drive Setup application located in your Utilities folder - I dunno what I'd do without partitions.
They can speed up access, but thats not really an issue - they allow you to have several different 'disks' and therefor backing up and erasing is easier. You can erase a partition without affecting the rest of the drive.
Its absolutely worth it. I have 3 HD's and 5 partitions - 3 of which are bootable.
Its pretty much fool proof. If one partition gets chewed, I can boot off others. If one HD gets chewed, I can boot of another.
Its really a necessity to me, but for most people, it isn't necessary.
You have to weigh up whether you need it. If not, don't bother.
If you do DV work this can be good - make a scratch partition you can erase regularly, and the smaller partitions, as I mentioned, can make for minutely faster access times... but not really
5. No idea. I'm not an OSX person. However, Preview should automatically handle them. Does the icons being different matter that much?
If so you can highlight one with a proper icon, hit Apple-I, click the icon, copy, click the one with the pictureviewer icon, click its icon in the Inspector window and paste.
6. No idea... try converting the .mov to a DV Stream (export from QuickTime Pro) - but, that'll chew HD space like theres no tomorrow.
7. You'll have to make them visible. Because they're on a CD, which is locked media, you can't make them visible. You'll need to use a program like Simple Browser (www.versiontracker.com) to try and copy them to your HD, then make them visible.
Is this in OSX or OS9? If OSX, use TinkerTool (www.versiontracker.com) to make all invisible files visible, and then copy them; or, use the terminal:
cp /Volumes/cdname/dir/to/file /Users/user/copy/to/here
8. Is this in OSX or OS9? OSX questions should be addressed in one of the OSX forums.
In OS9, I don't think you can. In OSX, hit Apple-J on a low-level directory, set the prefs, and hit the "copy to enclosed folders" button or whatever it is. I'm not in OSX right now so I'm not exactly sure...
9. If its the same on the Mac and the PC perhaps the file is corrupted. On the Mac, give RealPlayer more memory - though I doubt that'll help (it seems a problem with the media). RealPlayer is utter crap anyway.
10. Not as far as I know.