Can ayone help with the best way to restore my software function?

Question

Hi, I'm running OS 10.6.8 on an intel iMac.
I haven't done a software update for a while, due to poor connection speed, but last night, as the 'net was zipping along nicely for me, I installed all the latest reccommended updates, some via software update, but iTunes I downloaded from the apple download page.
When all the updates were installed, I restarted the Mac.
Now a large proportion of my applications, both native and non-apple, will not run.
I should add that I use firefox, and updated that last night as well.
I ran disk utility, and verified and repaired permissions. (A lot of repairs needed there!)
I tried to verify the hard drive, but it showed as needing repair, so I rebooted from my snow leopard install disc and ran the disk utility repair from there, successfully.
After I restarted in the usual manner, my software still won't run.
All I get is the "iTunes (or whatever app) quit unexpectedly" box. Hitting reopen from there just gives me the same again.
Do I need to go back and reinstall everything from scratch? OSX? Just the non-functioning apps?
The current hard drive is the third in this machine (iMac originially purchased at the start of 07).
Last time we replaced the drive was about this time last year.
I restored from time machine  - the last saved back-up from there was from July of last year, as for some reason, time machine had not worked properly in the interim - I think because the drive was too full, or some such.
Anyway, I was in the process of doing a complete reinstall, update and overhaul after getting the new hard drive.
We managed to savage some of the data from the old drive, so I was going to replace what files I could into the system, then erase my external hard drive and start time machine fresh. Trouble was, the family (and there's a lot of us) all jumped in and started using the machine before I got through updating everything and I got fed up trying to sort it out. I never started time machine again. I've backed up anything I wanted kept safe on an portable external drive and a couple of USBs. Therefore my more recent data is safe if I need to go back to that time cpsue back-up from last July.
Not sure about everyone elses. My external drive probably has enough space on it to copy pretty much everything from the main hard drive, but I can't use it via time capsule. It's the wrong format, and I dont want to lose the data I have already copied to it. I could just ignore the fact the others will lose their files, but I'm not that mean spirited, so will try to back up for htem if I can, before I do anything drastic.
If I have to erase and reinstall, is it possible first to just to copy the whole drive manually to the space on my portable drive, or should I just copy everyone's user files and the cntents of the shared folder?
I'm not hugely experienced in this, so I'd be grateful for any useful suggestions.
Thanks, in anticipation.
~ Betty.

Answer 1

Thanks. All your help is really appreciated. I wish I could report a better outcome.
I gave it a try. Got this:
while ! curl -C - -O 'http://supportdownload.apple.com/download.info.apple.com/Apple_Support_Area/Appl e_Software_Updates/Mac_OS_X/downloads/041-4966.20110725.gt5tv/MacOSXUpdCombo10. 6 .8.dmg'; do sleep 10; done
** Resuming transfer from byte position 299
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:--  0:00:02 --:--:--     0
curl: (33) HTTP server doesn't seem to support byte ranges. Cannot resume.
So, no luck there.
Sleep is always nice, but I don't find I need it ar 2.28 in the afternoon! I'm in Western Australia, so I'm guessing we're in vastly different time zones.
I'm currently attempting to get 10.6.7 combo via speed download. Thus far, 1.6% received in around half an hour. CUrrent estimated time remaining approx 33 hours!
No ethernet cable.
DSL is not available to me. I'm on a pair gain, so the only way for me to get broadband is via my wireless modem.
I tried to do network diagnostics when software updated kept failing.
It's very odd. External modem, which is what I'm using, is greyed out, so I can't select it.
No point checking the other options. Ethernet just tells me I'm not connected to ethernet or DSL, which I know. Airport wants me to select a network to join. What? I'm connected to the net NOW, via my external wireless modem. Airport is turned on, but that's only so that the other folks in my house, should they choose to do so, can connect their laptops via airport through this machine.
I've never had a problem with software update until I did the first download of the 10.6.8 combo, following the instllation of which, everything went kablooie.
I guess I'll just wait however long it takes for this speed download (not speedy, due to my currently restricted to dial-up speed isp account - but at least I can resume if interrupted) of 10.6.7 to finish and see how that goes. It could be another couple of days before I know.
Failing that, I think my next step is to go to my local Mac expert (shop 30 minutes drive from home) and see what he can suggest. It occurs to me that he may be able to give me the 10.6.8 combo on a disc or USB drive, so I can give it another try before we proceed to costly investigations. He may or may not charge me a little something for copying the .dmg file for me, but I really dont want to have to get into paying his hourly service rate for further work, if I can manage to sort it for myself. The thought of spending more money on this iMac after already replacing the hard drive (TWICE! - we're on HDD #3) holds ittle appeal. The machine is almost 6 years old. I really wish I could afford to upgrade.
I'll let you know if I have a breakthrough.
Thanks again.