MacBook 1.1 not booting up fully

Question

OK, here's my problem (narrative form - that's the way my mind works).
My MacBook is the original white version 1.1, 2GHz Intel Core Duo Processor with 1GB 667MHz DDR2 SDRAM (upgraded from the original 0.5 GB), bought on the day after its announcement by the late Mr Jobs in 2006 (my own use is a MacBook Pro late 2012 model with Mountain Lion - guess when I upgraded, and which one I'm using now?). It came with OSX 10.4 Tiger, which was gradually upgraded through the subset numbers, but stopped at the final upgrade by Apple to 10.4.11.
I have set up accounts for different users: an administrator account, one each for three children to have a personalised desktop etc., and an "Anyone" account for all other uses, my wife and me included. Up to a couple of weeks ago this setup was working fine and those using it were happy with it. We do have a Gates-crasher (sorry, Windows PC) laptop that is newer even than my "new" Mac, but nobody likes to use it if the MacBook is available. Am I surprised? No.
Unfortunately, now it won't boot up fully -- at least, it tries, but it takes so long to get there that I can't work out if it will ever complete the job. I have tried to get a Genius Bar appointment at my local (LiverpoolONE, UK) Mac Store, but there are none available for at least a week, and I am under pressure from the family to get it up and running again.
What happens now is that it gets to the "which account do you want to log into?" screen, but when you choose one of those it takes for ever to get the account fully loaded. Finder appears, but not the full range of icons at the top right hand side of the screen, nor the Dock. Then if you do try to do anything with what you get, it takes for ever for anything else to appear. For example, while I have been writing this and checking other parts of the support website it took probably 5 minutes or more for the "About this Mac" information to appear so that I could confirm the OSX version number, and in 10 minutes since I clicked on the "More Info ..." button, it has done nothing more than display the cycling micro-wheel beside the message, "Opening System Profiler.app". This is a machine that was working at full speed for its type not so long ago.
My suspicion is that something in the OS has got corrupted, so I wanted to see if a reinstall of that would help things out. Problem: can't find the original install-backup disk. It has been so reliable that I have only reinstalled once, after a mechanical hard-drive failure that meant a new HDD, over 5 years ago (I used to reinstall Windows several times a year before converting to Mac). We moved house since then ...
So I have ordered a replacement install disk - or rather, an upgrade to Snow Leopard, which I understand is the highest level of OS that will install on a MacBook 1.1.
My questions are:
(a) will this work on this machine - is my info that it will take Snow Leopard correct?
(b) if I run the install and find that it will go in (or any install, e.g. of Tiger 10.4.11 again), will the children lose their data, specifically the several years of digital photographs that are stored on the machine? Is there any way of avoiding this, given the snail's pace at which the machine is working just now?
(Please note: Yes, I do know about backing up, and am kicking myself now for having discontinued regular EHDD backups that I used to run on that machine when it was my working machine. No lectures, please, I have read them all to myself.)
Thanks for any help you can offer.

Answer 1

Your post says, "2. Power down your computer without shutting down through software." Does that mean hold down the on/off button for 5 secs so that it turns off without any of the software closing down?
If you have software running, you usually have an opportunity to back it up or recover data before shutting down.
command-option-escape and force quit everything that you can't otherwise quit manually.
If you are unable to boot it at all beyond the start screen, and can't see any files yet for over 10 minutes, yes, I mean hold down the power button until the power goes off.
Safari 4.1.3, and iTunes 9.2.1 are the only software Apple updates for 10.4.11 during 2010.  Everything else was updated prior to 2010.